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 $62.54   12.673%   $70.4657   $70.47   $70.45   $70.50  
  Purchase #2 $247.42   6.551%   $263.6285   $263.63   $263.65   $263.60  
  Purchase #3 $161.52   10.282%   $178.1275   $178.13   $178.15   $178.10  
  Purchase #4 $96.70   5.260%   $101.7864   $101.79   $101.80   $101.80  
  Purchase #5 $13.94   13.135%   $15.771   $15.77   $15.75   $15.80  
  Purchase #6 $202.27   6.696%   $215.814   $215.81   $215.80   $215.80  
  Purchase #7 $119.38   10.457%   $131.8636   $131.86   $131.85   $131.90  
  7 purchase totals = $903.77       $977.4567   $977.46   $977.45   $977.50