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 $226.67   3.562%   $234.744   $234.74   $234.75   $234.70  
  Purchase #2 $40.25   3.395%   $41.6165   $41.62   $41.60   $41.60  
  Purchase #3 $170.80   13.538%   $193.9229   $193.92   $193.90   $193.90  
  Purchase #4 $242.92   6.470%   $258.6369   $258.64   $258.65   $258.60  
  Purchase #5 $247.61   5.818%   $262.0159   $262.02   $262.00   $262.00  
  Purchase #6 $167.38   5.266%   $176.1942   $176.19   $176.20   $176.20  
  Purchase #7 $185.54   12.218%   $208.2093   $208.21   $208.20   $208.20  
  7 purchase totals = $1,281.17       $1,375.3397   $1,375.34   $1,375.30   $1,375.20