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 $84.96   4.717%   $88.9676   $88.97   $88.95   $89.00  
  Purchase #2 $119.31   6.406%   $126.953   $126.95   $126.95   $127.00  
  Purchase #3 $200.65   8.258%   $217.2197   $217.22   $217.20   $217.20  
  Purchase #4 $124.48   13.855%   $141.7267   $141.73   $141.75   $141.70  
  Purchase #5 $64.42   11.663%   $71.9333   $71.93   $71.95   $71.90  
  Purchase #6 $135.44   13.600%   $153.8598   $153.86   $153.85   $153.90  
  Purchase #7 $229.29   11.676%   $256.0619   $256.06   $256.05   $256.10  
  7 purchase totals = $958.55       $1,056.7220   $1,056.72   $1,056.70   $1,056.80