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 $38.64   11.652%   $43.1423   $43.14   $43.15   $43.10  
  Purchase #2 $102.52   6.655%   $109.3427   $109.34   $109.35   $109.30  
  Purchase #3 $191.50   5.709%   $202.4327   $202.43   $202.45   $202.40  
  Purchase #4 $18.99   4.290%   $19.8047   $19.80   $19.80   $19.80  
  Purchase #5 $160.35   4.643%   $167.7951   $167.80   $167.80   $167.80  
  Purchase #6 $132.92   3.511%   $137.5868   $137.59   $137.60   $137.60  
  Purchase #7 $88.71   5.833%   $93.8845   $93.88   $93.90   $93.90  
  7 purchase totals = $733.63       $773.9888   $773.98   $774.05   $773.90