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 $222.74   10.591%   $246.3304   $246.33   $246.35   $246.30  
  Purchase #2 $175.75   10.441%   $194.1001   $194.10   $194.10   $194.10  
  Purchase #3 $198.44   11.120%   $220.5065   $220.51   $220.50   $220.50  
  Purchase #4 $151.58   4.466%   $158.3496   $158.35   $158.35   $158.30  
  Purchase #5 $205.62   3.198%   $212.1957   $212.20   $212.20   $212.20  
  Purchase #6 $48.69   4.678%   $50.9677   $50.97   $50.95   $51.00  
  Purchase #7 $135.67   11.453%   $151.2083   $151.21   $151.20   $151.20  
  7 purchase totals = $1,138.49       $1,233.6583   $1,233.67   $1,233.65   $1,233.60