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 $95.67   5.721%   $101.1433   $101.14   $101.15   $101.10  
  Purchase #2 $44.48   10.168%   $49.0027   $49.00   $49.00   $49.00  
  Purchase #3 $201.74   8.809%   $219.5113   $219.51   $219.50   $219.50  
  Purchase #4 $51.95   8.845%   $56.545   $56.55   $56.55   $56.50  
  Purchase #5 $217.75   5.311%   $229.3147   $229.31   $229.30   $229.30  
  Purchase #6 $24.65   6.336%   $26.2118   $26.21   $26.20   $26.20  
  Purchase #7 $92.26   8.678%   $100.2663   $100.27   $100.25   $100.30  
  7 purchase totals = $728.50       $781.9951   $781.99   $781.95   $781.90