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 $33.79   6.373%   $35.9434   $35.94   $35.95   $35.90  
  Purchase #2 $96.59   5.556%   $101.9565   $101.96   $101.95   $102.00  
  Purchase #3 $113.86   5.269%   $119.8593   $119.86   $119.85   $119.90  
  Purchase #4 $233.80   11.455%   $260.5818   $260.58   $260.60   $260.60  
  Purchase #5 $108.85   9.563%   $119.2593   $119.26   $119.25   $119.30  
  Purchase #6 $206.94   3.137%   $213.4317   $213.43   $213.45   $213.40  
  Purchase #7 $26.94   8.730%   $29.2919   $29.29   $29.30   $29.30  
  7 purchase totals = $820.77       $880.3239   $880.32   $880.35   $880.40