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 $67.57   5.752%   $71.4566   $71.46   $71.45   $71.50  
  Purchase #2 $124.73   13.293%   $141.3104   $141.31   $141.30   $141.30  
  Purchase #3 $161.38   7.702%   $173.8095   $173.81   $173.80   $173.80  
  Purchase #4 $36.40   3.340%   $37.6158   $37.62   $37.60   $37.60  
  Purchase #5 $8.96   10.605%   $9.9102   $9.91   $9.90   $9.90  
  Purchase #6 $227.50   3.256%   $234.9074   $234.91   $234.90   $234.90  
  Purchase #7 $149.98   5.200%   $157.779   $157.78   $157.80   $157.80  
  7 purchase totals = $776.52       $826.7889   $826.80   $826.75   $826.80