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 $129.86   12.521%   $146.1198   $146.12   $146.10   $146.10  
  Purchase #2 $32.26   3.215%   $33.2972   $33.30   $33.30   $33.30  
  Purchase #3 $241.28   6.346%   $256.5916   $256.59   $256.60   $256.60  
  Purchase #4 $168.80   7.484%   $181.433   $181.43   $181.45   $181.40  
  Purchase #5 $195.68   11.366%   $217.921   $217.92   $217.90   $217.90  
  Purchase #6 $141.95   12.642%   $159.8953   $159.90   $159.90   $159.90  
  Purchase #7 $213.35   9.768%   $234.19   $234.19   $234.20   $234.20  
  7 purchase totals = $1,123.18       $1,229.4479   $1,229.45   $1,229.45   $1,229.40