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 $130.64   10.738%   $144.6681   $144.67   $144.65   $144.70  
  Purchase #2 $69.88   5.156%   $73.483   $73.48   $73.50   $73.50  
  Purchase #3 $65.53   8.172%   $70.8851   $70.89   $70.90   $70.90  
  Purchase #4 $189.82   8.873%   $206.6627   $206.66   $206.65   $206.70  
  Purchase #5 $205.64   11.849%   $230.0063   $230.01   $230.00   $230.00  
  Purchase #6 $77.29   7.419%   $83.0241   $83.02   $83.00   $83.00  
  Purchase #7 $188.26   13.228%   $213.163   $213.16   $213.15   $213.20  
  7 purchase totals = $927.06       $1,021.8923   $1,021.89   $1,021.85   $1,022.00