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 $64.95   6.157%   $68.949   $68.95   $68.95   $68.90  
  Purchase #2 $33.53   7.265%   $35.966   $35.97   $35.95   $36.00  
  Purchase #3 $133.63   11.258%   $148.6741   $148.67   $148.65   $148.70  
  Purchase #4 $180.58   6.117%   $191.6261   $191.63   $191.65   $191.60  
  Purchase #5 $157.69   4.245%   $164.3839   $164.38   $164.40   $164.40  
  Purchase #6 $37.82   8.294%   $40.9568   $40.96   $40.95   $41.00  
  Purchase #7 $39.75   12.599%   $44.7581   $44.76   $44.75   $44.80  
  7 purchase totals = $647.95       $695.3140   $695.32   $695.30   $695.40