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 $238.98   11.167%   $265.6669   $265.67   $265.65   $265.70  
  Purchase #2 $229.71   5.488%   $242.3165   $242.32   $242.30   $242.30  
  Purchase #3 $169.92   12.251%   $190.7369   $190.74   $190.75   $190.70  
  Purchase #4 $32.59   5.160%   $34.2716   $34.27   $34.25   $34.30  
  Purchase #5 $233.82   7.592%   $251.5716   $251.57   $251.55   $251.60  
  Purchase #6 $66.55   12.632%   $74.9566   $74.96   $74.95   $75.00  
  Purchase #7 $132.54   10.380%   $146.2977   $146.30   $146.30   $146.30  
  7 purchase totals = $1,104.11       $1,205.8178   $1,205.83   $1,205.75   $1,205.90