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 $224.84   12.409%   $252.7404   $252.74   $252.75   $252.70  
  Purchase #2 $177.76   9.119%   $193.9699   $193.97   $193.95   $194.00  
  Purchase #3 $133.41   7.217%   $143.0382   $143.04   $143.05   $143.00  
  Purchase #4 $75.84   11.580%   $84.6223   $84.62   $84.60   $84.60  
  Purchase #5 $141.58   5.458%   $149.3074   $149.31   $149.30   $149.30  
  Purchase #6 $78.82   13.529%   $89.4836   $89.48   $89.50   $89.50  
  Purchase #7 $124.70   8.740%   $135.5988   $135.60   $135.60   $135.60  
  7 purchase totals = $956.95       $1,048.7606   $1,048.76   $1,048.75   $1,048.70