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 $46.71   10.739%   $51.7262   $51.73   $51.75   $51.70  
  Purchase #2 $233.65   6.255%   $248.2648   $248.26   $248.25   $248.30  
  Purchase #3 $228.33   10.867%   $253.1426   $253.14   $253.15   $253.10  
  Purchase #4 $90.87   7.825%   $97.9806   $97.98   $98.00   $98.00  
  Purchase #5 $101.92   5.566%   $107.5929   $107.59   $107.60   $107.60  
  Purchase #6 $87.35   6.418%   $92.9561   $92.96   $92.95   $93.00  
  Purchase #7 $174.73   8.282%   $189.2011   $189.20   $189.20   $189.20  
  7 purchase totals = $963.56       $1,040.8643   $1,040.86   $1,040.90   $1,040.90