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 $165.82   11.551%   $184.9739   $184.97   $184.95   $185.00  
  Purchase #2 $211.79   11.125%   $235.3516   $235.35   $235.35   $235.40  
  Purchase #3 $92.63   5.287%   $97.5273   $97.53   $97.55   $97.50  
  Purchase #4 $104.42   4.344%   $108.956   $108.96   $108.95   $109.00  
  Purchase #5 $235.84   9.612%   $258.5089   $258.51   $258.50   $258.50  
  Purchase #6 $224.61   11.858%   $251.2443   $251.24   $251.25   $251.20  
  Purchase #7 $169.99   4.275%   $177.2571   $177.26   $177.25   $177.30  
  7 purchase totals = $1,205.10       $1,313.8191   $1,313.82   $1,313.80   $1,313.90