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 $40.90   7.469%   $43.9548   $43.95   $43.95   $44.00  
  Purchase #2 $230.74   12.816%   $260.3116   $260.31   $260.30   $260.30  
  Purchase #3 $158.52   6.305%   $168.5147   $168.51   $168.50   $168.50  
  Purchase #4 $91.65   5.151%   $96.3709   $96.37   $96.35   $96.40  
  Purchase #5 $164.66   6.851%   $175.9409   $175.94   $175.95   $175.90  
  Purchase #6 $119.93   3.700%   $124.3674   $124.37   $124.35   $124.40  
  Purchase #7 $154.92   7.756%   $166.9356   $166.94   $166.95   $166.90  
  7 purchase totals = $961.32       $1,036.3959   $1,036.39   $1,036.35   $1,036.40