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 $227.74   7.106%   $243.9232   $243.92   $243.90   $243.90  
  Purchase #2 $57.67   12.661%   $64.9716   $64.97   $64.95   $65.00  
  Purchase #3 $167.96   4.513%   $175.54   $175.54   $175.55   $175.50  
  Purchase #4 $199.83   9.504%   $218.8218   $218.82   $218.80   $218.80  
  Purchase #5 $157.42   4.589%   $164.644   $164.64   $164.65   $164.60  
  Purchase #6 $162.52   9.870%   $178.5607   $178.56   $178.55   $178.60  
  Purchase #7 $182.25   3.216%   $188.1112   $188.11   $188.10   $188.10  
  7 purchase totals = $1,155.39       $1,234.5725   $1,234.56   $1,234.50   $1,234.50