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 $82.94   13.773%   $94.3633   $94.36   $94.35   $94.40  
  Purchase #2 $125.71   3.424%   $130.0143   $130.01   $130.00   $130.00  
  Purchase #3 $175.25   9.714%   $192.2738   $192.27   $192.25   $192.30  
  Purchase #4 $127.46   4.113%   $132.7024   $132.70   $132.70   $132.70  
  Purchase #5 $29.64   10.357%   $32.7098   $32.71   $32.70   $32.70  
  Purchase #6 $247.35   8.536%   $268.4638   $268.46   $268.45   $268.50  
  Purchase #7 $35.97   10.754%   $39.8382   $39.84   $39.85   $39.80  
  7 purchase totals = $824.32       $890.3656   $890.35   $890.30   $890.40