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 $49.34   4.850%   $51.733   $51.73   $51.75   $51.70  
  Purchase #2 $73.41   10.695%   $81.2612   $81.26   $81.25   $81.30  
  Purchase #3 $74.71   13.356%   $84.6883   $84.69   $84.70   $84.70  
  Purchase #4 $220.36   10.399%   $243.2752   $243.28   $243.30   $243.30  
  Purchase #5 $57.29   8.649%   $62.245   $62.25   $62.25   $62.20  
  Purchase #6 $248.31   6.112%   $263.4867   $263.49   $263.50   $263.50  
  Purchase #7 $160.55   10.304%   $177.0931   $177.09   $177.10   $177.10  
  7 purchase totals = $883.97       $963.7825   $963.79   $963.85   $963.80