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 $205.79   12.681%   $231.8862   $231.89   $231.90   $231.90  
  Purchase #2 $148.50   4.504%   $155.1884   $155.19   $155.20   $155.20  
  Purchase #3 $24.29   8.153%   $26.2704   $26.27   $26.25   $26.30  
  Purchase #4 $119.38   3.382%   $123.4174   $123.42   $123.40   $123.40  
  Purchase #5 $105.25   3.840%   $109.2916   $109.29   $109.30   $109.30  
  Purchase #6 $73.47   5.731%   $77.6806   $77.68   $77.70   $77.70  
  Purchase #7 $32.56   11.589%   $36.3334   $36.33   $36.35   $36.30  
  7 purchase totals = $709.24       $760.0680   $760.07   $760.10   $760.10