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	$7.33	6.811%	$7.8292	$7.83	$7.85	$7.80
Purchase #2	$169.98	12.421%	$191.0932	$191.09	$191.10	$191.10
Purchase #3	$140.45	12.726%	$158.3237	$158.32	$158.30	$158.30
Purchase #4	$57.39	9.522%	$62.8547	$62.85	$62.85	$62.90
Purchase #5	$5.87	5.349%	$6.184	$6.18	$6.20	$6.20
Purchase #6	$224.33	11.764%	$250.7202	$250.72	$250.70	$250.70
Purchase #7	$66.89	6.156%	$71.0077	$71.01	$71.00	$71.00
7 purchase totals =	$672.24		$748.0127	$748.00	$748.00	$748.00