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 $45.58   7.754%   $49.1143   $49.11   $49.10   $49.10  
  Purchase #2 $195.28   6.436%   $207.8482   $207.85   $207.85   $207.80  
  Purchase #3 $235.39   13.451%   $267.0523   $267.05   $267.05   $267.10  
  Purchase #4 $26.81   6.804%   $28.6342   $28.63   $28.65   $28.60  
  Purchase #5 $94.71   3.456%   $97.9832   $97.98   $98.00   $98.00  
  Purchase #6 $107.34   10.454%   $118.5613   $118.56   $118.55   $118.60  
  Purchase #7 $29.61   8.563%   $32.1455   $32.15   $32.15   $32.10  
  7 purchase totals = $734.72       $801.3390   $801.33   $801.35   $801.30