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 $239.34   13.351%   $271.2943   $271.29   $271.30   $271.30  
  Purchase #2 $186.61   8.374%   $202.2367   $202.24   $202.25   $202.20  
  Purchase #3 $42.82   11.613%   $47.7927   $47.79   $47.80   $47.80  
  Purchase #4 $213.90   11.498%   $238.4942   $238.49   $238.50   $238.50  
  Purchase #5 $46.94   3.163%   $48.4247   $48.42   $48.40   $48.40  
  Purchase #6 $43.66   9.153%   $47.6562   $47.66   $47.65   $47.70  
  Purchase #7 $175.32   11.221%   $194.9927   $194.99   $195.00   $195.00  
  7 purchase totals = $948.59       $1,050.8915   $1,050.88   $1,050.90   $1,050.90