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 $56.49   9.396%   $61.7978   $61.80   $61.80   $61.80  
  Purchase #2 $169.54   5.360%   $178.6273   $178.63   $178.65   $178.60  
  Purchase #3 $178.98   8.182%   $193.6241   $193.62   $193.60   $193.60  
  Purchase #4 $33.67   8.803%   $36.634   $36.63   $36.65   $36.60  
  Purchase #5 $245.48   11.663%   $274.1103   $274.11   $274.10   $274.10  
  Purchase #6 $57.81   8.121%   $62.5048   $62.50   $62.50   $62.50  
  Purchase #7 $84.82   12.673%   $95.5692   $95.57   $95.55   $95.60  
  7 purchase totals = $826.79       $902.8675   $902.86   $902.85   $902.80