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 $108.71   9.227%   $118.7407   $118.74   $118.75   $118.70  
  Purchase #2 $217.46   12.271%   $244.1445   $244.14   $244.15   $244.10  
  Purchase #3 $145.58   5.555%   $153.667   $153.67   $153.65   $153.70  
  Purchase #4 $66.26   10.842%   $73.4439   $73.44   $73.45   $73.40  
  Purchase #5 $29.88   8.153%   $32.3161   $32.32   $32.30   $32.30  
  Purchase #6 $222.38   12.279%   $249.686   $249.69   $249.70   $249.70  
  Purchase #7 $21.50   13.654%   $24.4356   $24.44   $24.45   $24.40  
  7 purchase totals = $811.77       $896.4338   $896.44   $896.45   $896.30