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 $87.59   12.419%   $98.4678   $98.47   $98.45   $98.50  
  Purchase #2 $176.89   8.874%   $192.5872   $192.59   $192.60   $192.60  
  Purchase #3 $130.84   13.642%   $148.6892   $148.69   $148.70   $148.70  
  Purchase #4 $210.29   13.161%   $237.9663   $237.97   $237.95   $238.00  
  Purchase #5 $83.50   10.468%   $92.2408   $92.24   $92.25   $92.20  
  Purchase #6 $130.26   5.713%   $137.7018   $137.70   $137.70   $137.70  
  Purchase #7 $175.39   10.796%   $194.3251   $194.33   $194.35   $194.30  
  7 purchase totals = $994.76       $1,101.9782   $1,101.99   $1,102.00   $1,102.00