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 $62.60   13.757%   $71.2119   $71.21   $71.20   $71.20  
  Purchase #2 $46.50   10.423%   $51.3467   $51.35   $51.35   $51.30  
  Purchase #3 $247.84   7.220%   $265.734   $265.73   $265.75   $265.70  
  Purchase #4 $245.34   7.324%   $263.3087   $263.31   $263.30   $263.30  
  Purchase #5 $156.30   3.707%   $162.094   $162.09   $162.10   $162.10  
  Purchase #6 $62.88   3.556%   $65.116   $65.12   $65.10   $65.10  
  Purchase #7 $8.31   6.391%   $8.8411   $8.84   $8.85   $8.80  
  7 purchase totals = $829.77       $887.6524   $887.65   $887.65   $887.50