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 $202.81   12.584%   $228.3316   $228.33   $228.35   $228.30  
  Purchase #2 $43.61   12.211%   $48.9352   $48.94   $48.95   $48.90  
  Purchase #3 $5.59   5.766%   $5.9123   $5.91   $5.90   $5.90  
  Purchase #4 $84.87   9.385%   $92.835   $92.84   $92.85   $92.80  
  Purchase #5 $242.73   10.348%   $267.8477   $267.85   $267.85   $267.80  
  Purchase #6 $164.46   6.756%   $175.5709   $175.57   $175.55   $175.60  
  Purchase #7 $182.25   8.240%   $197.2674   $197.27   $197.25   $197.30  
  7 purchase totals = $926.32       $1,016.7001   $1,016.71   $1,016.70   $1,016.60