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 $202.37   13.165%   $229.012   $229.01   $229.00   $229.00  
  Purchase #2 $242.51   12.754%   $273.4397   $273.44   $273.45   $273.40  
  Purchase #3 $47.35   4.870%   $49.6559   $49.66   $49.65   $49.70  
  Purchase #4 $209.76   4.218%   $218.6077   $218.61   $218.60   $218.60  
  Purchase #5 $249.56   10.559%   $275.911   $275.91   $275.90   $275.90  
  Purchase #6 $130.54   11.261%   $145.2401   $145.24   $145.25   $145.20  
  Purchase #7 $85.55   6.598%   $91.1946   $91.19   $91.20   $91.20  
  7 purchase totals = $1,167.64       $1,283.0610   $1,283.06   $1,283.05   $1,283.00