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 $62.39   10.576%   $68.9884   $68.99   $69.00   $69.00  
  Purchase #2 $207.88   3.839%   $215.8605   $215.86   $215.85   $215.90  
  Purchase #3 $58.51   9.335%   $63.9719   $63.97   $63.95   $64.00  
  Purchase #4 $172.65   8.209%   $186.8228   $186.82   $186.80   $186.80  
  Purchase #5 $102.26   5.591%   $107.9774   $107.98   $108.00   $108.00  
  Purchase #6 $9.33   4.198%   $9.7217   $9.72   $9.70   $9.70  
  Purchase #7 $217.40   12.846%   $245.3272   $245.33   $245.35   $245.30  
  7 purchase totals = $830.42       $898.6699   $898.67   $898.65   $898.70