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 $44.31   9.677%   $48.5979   $48.60   $48.60   $48.60  
  Purchase #2 $143.25   10.531%   $158.3357   $158.34   $158.35   $158.30  
  Purchase #3 $61.99   10.502%   $68.5002   $68.50   $68.50   $68.50  
  Purchase #4 $114.30   11.648%   $127.6137   $127.61   $127.60   $127.60  
  Purchase #5 $107.65   9.111%   $117.458   $117.46   $117.45   $117.50  
  Purchase #6 $103.39   12.162%   $115.9643   $115.96   $115.95   $116.00  
  Purchase #7 $200.85   5.554%   $212.0052   $212.01   $212.00   $212.00  
  7 purchase totals = $775.74       $848.4750   $848.48   $848.45   $848.50