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 $207.38   13.281%   $234.9221   $234.92   $234.90   $234.90  
  Purchase #2 $112.92   7.536%   $121.4297   $121.43   $121.45   $121.40  
  Purchase #3 $26.80   10.472%   $29.6065   $29.61   $29.60   $29.60  
  Purchase #4 $206.79   13.874%   $235.48   $235.48   $235.50   $235.50  
  Purchase #5 $85.44   10.536%   $94.442   $94.44   $94.45   $94.40  
  Purchase #6 $227.79   11.667%   $254.3663   $254.37   $254.35   $254.40  
  Purchase #7 $91.77   4.631%   $96.0199   $96.02   $96.00   $96.00  
  7 purchase totals = $958.89       $1,066.2665   $1,066.27   $1,066.25   $1,066.20