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 $61.34   11.708%   $68.5217   $68.52   $68.50   $68.50  
  Purchase #2 $159.77   11.421%   $178.0173   $178.02   $178.00   $178.00  
  Purchase #3 $198.74   5.436%   $209.5435   $209.54   $209.55   $209.50  
  Purchase #4 $211.42   3.564%   $218.955   $218.96   $218.95   $219.00  
  Purchase #5 $138.38   13.299%   $156.7832   $156.78   $156.80   $156.80  
  Purchase #6 $136.73   8.578%   $148.4587   $148.46   $148.45   $148.50  
  Purchase #7 $250.28   7.228%   $268.3702   $268.37   $268.35   $268.40  
  7 purchase totals = $1,156.66       $1,248.6496   $1,248.65   $1,248.60   $1,248.70