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 $221.95   10.764%   $245.8407   $245.84   $245.85   $245.80  
  Purchase #2 $16.87   8.354%   $18.2793   $18.28   $18.30   $18.30  
  Purchase #3 $125.96   11.799%   $140.822   $140.82   $140.80   $140.80  
  Purchase #4 $48.44   4.349%   $50.5467   $50.55   $50.55   $50.50  
  Purchase #5 $247.76   5.160%   $260.5444   $260.54   $260.55   $260.50  
  Purchase #6 $62.73   8.225%   $67.8895   $67.89   $67.90   $67.90  
  Purchase #7 $195.57   11.293%   $217.6557   $217.66   $217.65   $217.70  
  7 purchase totals = $919.28       $1,001.5783   $1,001.58   $1,001.60   $1,001.50