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 $86.60   9.409%   $94.7482   $94.75   $94.75   $94.70  
  Purchase #2 $247.43   12.252%   $277.7451   $277.75   $277.75   $277.70  
  Purchase #3 $180.91   10.244%   $199.4424   $199.44   $199.45   $199.40  
  Purchase #4 $156.90   13.809%   $178.5663   $178.57   $178.55   $178.60  
  Purchase #5 $90.68   10.121%   $99.8577   $99.86   $99.85   $99.90  
  Purchase #6 $95.66   7.182%   $102.5303   $102.53   $102.55   $102.50  
  Purchase #7 $13.90   10.175%   $15.3143   $15.31   $15.30   $15.30  
  7 purchase totals = $872.08       $968.2043   $968.21   $968.20   $968.10