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 $62.29   4.543%   $65.1198   $65.12   $65.10   $65.10  
  Purchase #2 $152.88   6.134%   $162.2577   $162.26   $162.25   $162.30  
  Purchase #3 $133.36   6.146%   $141.5563   $141.56   $141.55   $141.60  
  Purchase #4 $203.76   11.623%   $227.443   $227.44   $227.45   $227.40  
  Purchase #5 $38.28   13.293%   $43.3686   $43.37   $43.35   $43.40  
  Purchase #6 $83.45   12.289%   $93.7052   $93.71   $93.70   $93.70  
  Purchase #7 $127.43   4.213%   $132.7986   $132.80   $132.80   $132.80  
  7 purchase totals = $801.45       $866.2492   $866.26   $866.20   $866.30