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 $194.93   6.208%   $207.0313   $207.03   $207.05   $207.00  
  Purchase #2 $100.96   6.233%   $107.2528   $107.25   $107.25   $107.30  
  Purchase #3 $92.46   6.808%   $98.7547   $98.75   $98.75   $98.80  
  Purchase #4 $236.95   8.170%   $256.3088   $256.31   $256.30   $256.30  
  Purchase #5 $13.63   11.567%   $15.2066   $15.21   $15.20   $15.20  
  Purchase #6 $166.45   9.116%   $181.6236   $181.62   $181.60   $181.60  
  Purchase #7 $243.45   10.487%   $268.9806   $268.98   $269.00   $269.00  
  7 purchase totals = $1,048.83       $1,135.1584   $1,135.15   $1,135.15   $1,135.20