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 $65.61   12.221%   $73.6282   $73.63   $73.65   $73.60  
  Purchase #2 $227.26   13.561%   $258.0787   $258.08   $258.10   $258.10  
  Purchase #3 $92.40   7.638%   $99.4575   $99.46   $99.45   $99.50  
  Purchase #4 $175.93   7.773%   $189.605   $189.61   $189.60   $189.60  
  Purchase #5 $9.99   9.581%   $10.9471   $10.95   $10.95   $10.90  
  Purchase #6 $202.38   6.414%   $215.3607   $215.36   $215.35   $215.40  
  Purchase #7 $146.85   6.291%   $156.0883   $156.09   $156.10   $156.10  
  7 purchase totals = $920.42       $1,003.1655   $1,003.18   $1,003.20   $1,003.20