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 $58.40   13.638%   $66.3646   $66.36   $66.35   $66.40  
  Purchase #2 $220.94   12.683%   $248.9618   $248.96   $248.95   $249.00  
  Purchase #3 $69.57   7.506%   $74.7919   $74.79   $74.80   $74.80  
  Purchase #4 $208.98   13.451%   $237.0899   $237.09   $237.10   $237.10  
  Purchase #5 $150.48   9.797%   $165.2225   $165.22   $165.20   $165.20  
  Purchase #6 $5.98   3.291%   $6.1768   $6.18   $6.20   $6.20  
  Purchase #7 $50.94   4.649%   $53.3082   $53.31   $53.30   $53.30  
  7 purchase totals = $765.29       $851.9157   $851.91   $851.90   $852.00