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 $95.58   7.492%   $102.7409   $102.74   $102.75   $102.70  
  Purchase #2 $84.33   11.432%   $93.9706   $93.97   $93.95   $94.00  
  Purchase #3 $237.75   10.326%   $262.3001   $262.30   $262.30   $262.30  
  Purchase #4 $161.46   12.821%   $182.1608   $182.16   $182.15   $182.20  
  Purchase #5 $19.82   9.113%   $21.6262   $21.63   $21.65   $21.60  
  Purchase #6 $33.79   4.559%   $35.3305   $35.33   $35.35   $35.30  
  Purchase #7 $214.82   6.408%   $228.5857   $228.59   $228.60   $228.60  
  7 purchase totals = $847.55       $926.7148   $926.72   $926.75   $926.70