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 $42.67   8.511%   $46.3016   $46.30   $46.30   $46.30  
  Purchase #2 $239.31   13.623%   $271.9112   $271.91   $271.90   $271.90  
  Purchase #3 $189.27   10.821%   $209.7509   $209.75   $209.75   $209.80  
  Purchase #4 $132.69   8.449%   $143.901   $143.90   $143.90   $143.90  
  Purchase #5 $76.78   6.614%   $81.8582   $81.86   $81.85   $81.90  
  Purchase #6 $235.42   5.777%   $249.0202   $249.02   $249.00   $249.00  
  Purchase #7 $29.80   5.193%   $31.3475   $31.35   $31.35   $31.30  
  7 purchase totals = $945.94       $1,034.0906   $1,034.09   $1,034.05   $1,034.10