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 $134.30   13.145%   $151.9537   $151.95   $151.95   $152.00  
  Purchase #2 $226.68   9.130%   $247.3759   $247.38   $247.40   $247.40  
  Purchase #3 $25.38   7.609%   $27.3112   $27.31   $27.30   $27.30  
  Purchase #4 $247.82   7.134%   $265.4995   $265.50   $265.50   $265.50  
  Purchase #5 $50.76   4.151%   $52.867   $52.87   $52.85   $52.90  
  Purchase #6 $176.89   9.569%   $193.8166   $193.82   $193.80   $193.80  
  Purchase #7 $52.44   9.194%   $57.2613   $57.26   $57.25   $57.30  
  7 purchase totals = $914.27       $996.0852   $996.09   $996.05   $996.20