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 $29.83   13.751%   $33.9319   $33.93   $33.95   $33.90  
  Purchase #2 $241.38   10.102%   $265.7642   $265.76   $265.75   $265.80  
  Purchase #3 $74.40   3.348%   $76.8909   $76.89   $76.90   $76.90  
  Purchase #4 $82.64   7.512%   $88.8479   $88.85   $88.85   $88.80  
  Purchase #5 $202.99   3.610%   $210.3179   $210.32   $210.30   $210.30  
  Purchase #6 $79.25   6.381%   $84.3069   $84.31   $84.30   $84.30  
  Purchase #7 $213.60   13.770%   $243.0127   $243.01   $243.00   $243.00  
  7 purchase totals = $924.09       $1,003.0724   $1,003.07   $1,003.05   $1,003.00