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 $142.26   6.381%   $151.3376   $151.34   $151.35   $151.30  
  Purchase #2 $101.47   10.265%   $111.8859   $111.89   $111.90   $111.90  
  Purchase #3 $98.26   8.622%   $106.732   $106.73   $106.75   $106.70  
  Purchase #4 $232.38   6.277%   $246.9665   $246.97   $246.95   $247.00  
  Purchase #5 $88.97   6.124%   $94.4185   $94.42   $94.40   $94.40  
  Purchase #6 $207.44   12.562%   $233.4986   $233.50   $233.50   $233.50  
  Purchase #7 $172.38   9.286%   $188.3872   $188.39   $188.40   $188.40  
  7 purchase totals = $1,043.16       $1,133.2263   $1,133.24   $1,133.25   $1,133.20