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 $224.86   9.770%   $246.8288   $246.83   $246.85   $246.80  
  Purchase #2 $108.98   7.672%   $117.3409   $117.34   $117.35   $117.30  
  Purchase #3 $167.69   7.673%   $180.5569   $180.56   $180.55   $180.60  
  Purchase #4 $52.71   11.799%   $58.9293   $58.93   $58.95   $58.90  
  Purchase #5 $177.35   10.387%   $195.7713   $195.77   $195.75   $195.80  
  Purchase #6 $36.89   13.361%   $41.8189   $41.82   $41.80   $41.80  
  Purchase #7 $79.28   6.472%   $84.411   $84.41   $84.40   $84.40  
  7 purchase totals = $847.76       $925.6571   $925.66   $925.65   $925.60