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 $61.57   7.760%   $66.3478   $66.35   $66.35   $66.30  
  Purchase #2 $242.52   12.132%   $271.9425   $271.94   $271.95   $271.90  
  Purchase #3 $26.78   6.134%   $28.4227   $28.42   $28.40   $28.40  
  Purchase #4 $219.54   10.152%   $241.8277   $241.83   $241.85   $241.80  
  Purchase #5 $245.69   8.423%   $266.3845   $266.38   $266.40   $266.40  
  Purchase #6 $128.32   6.777%   $137.0162   $137.02   $137.00   $137.00  
  Purchase #7 $199.35   5.185%   $209.6863   $209.69   $209.70   $209.70  
  7 purchase totals = $1,123.77       $1,221.6277   $1,221.63   $1,221.65   $1,221.50