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 $182.68   13.318%   $207.0093   $207.01   $207.00   $207.00  
  Purchase #2 $113.29   10.369%   $125.037   $125.04   $125.05   $125.00  
  Purchase #3 $139.45   5.158%   $146.6428   $146.64   $146.65   $146.60  
  Purchase #4 $43.54   10.848%   $48.2632   $48.26   $48.25   $48.30  
  Purchase #5 $115.78   12.662%   $130.4401   $130.44   $130.45   $130.40  
  Purchase #6 $135.73   4.367%   $141.6573   $141.66   $141.65   $141.70  
  Purchase #7 $186.70   8.299%   $202.1942   $202.19   $202.20   $202.20  
  7 purchase totals = $917.17       $1,001.2439   $1,001.24   $1,001.25   $1,001.20