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 $66.88   10.540%   $73.9292   $73.93   $73.95   $73.90  
  Purchase #2 $35.48   3.622%   $36.7651   $36.77   $36.75   $36.80  
  Purchase #3 $246.81   8.351%   $267.4211   $267.42   $267.40   $267.40  
  Purchase #4 $155.95   7.131%   $167.0708   $167.07   $167.05   $167.10  
  Purchase #5 $67.74   13.567%   $76.9303   $76.93   $76.95   $76.90  
  Purchase #6 $58.86   7.146%   $63.0661   $63.07   $63.05   $63.10  
  Purchase #7 $124.77   11.143%   $138.6731   $138.67   $138.65   $138.70  
  7 purchase totals = $756.49       $823.8557   $823.86   $823.80   $823.90