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 $79.38   7.306%   $85.1795   $85.18   $85.20   $85.20  
  Purchase #2 $215.88   8.591%   $234.4263   $234.43   $234.45   $234.40  
  Purchase #3 $88.36   8.222%   $95.625   $95.63   $95.65   $95.60  
  Purchase #4 $95.32   13.221%   $107.9223   $107.92   $107.90   $107.90  
  Purchase #5 $86.95   10.219%   $95.8354   $95.84   $95.85   $95.80  
  Purchase #6 $174.33   13.382%   $197.6588   $197.66   $197.65   $197.70  
  Purchase #7 $222.95   10.657%   $246.7098   $246.71   $246.70   $246.70  
  7 purchase totals = $963.17       $1,063.3571   $1,063.37   $1,063.40   $1,063.30