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 $56.47   4.393%   $58.9507   $58.95   $58.95   $59.00  
  Purchase #2 $148.52   9.609%   $162.7913   $162.79   $162.80   $162.80  
  Purchase #3 $90.92   11.539%   $101.4113   $101.41   $101.40   $101.40  
  Purchase #4 $137.25   10.278%   $151.3566   $151.36   $151.35   $151.40  
  Purchase #5 $67.73   13.454%   $76.8424   $76.84   $76.85   $76.80  
  Purchase #6 $215.26   12.755%   $242.7164   $242.72   $242.70   $242.70  
  Purchase #7 $141.97   7.257%   $152.2728   $152.27   $152.25   $152.30  
  7 purchase totals = $858.12       $946.3415   $946.34   $946.30   $946.40