Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $170.32   13.293%   $192.9606   $192.96   $192.95   $193.00  
  Purchase #2 $129.26   3.357%   $133.5993   $133.60   $133.60   $133.60  
  Purchase #3 $124.82   13.442%   $141.5983   $141.60   $141.60   $141.60  
  Purchase #4 $245.99   10.539%   $271.9149   $271.91   $271.90   $271.90  
  Purchase #5 $193.88   4.359%   $202.3312   $202.33   $202.35   $202.30  
  Purchase #6 $216.31   5.853%   $228.9706   $228.97   $228.95   $229.00  
  Purchase #7 $112.79   12.285%   $126.6463   $126.65   $126.65   $126.60  
  7 purchase totals = $1,193.37       $1,298.0212   $1,298.02   $1,298.00   $1,298.00