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	$37.92	7.406%	$40.7284	$40.73	$40.75	$40.70
Purchase #2	$110.56	12.625%	$124.5182	$124.52	$124.50	$124.50
Purchase #3	$75.49	11.113%	$83.8792	$83.88	$83.90	$83.90
Purchase #4	$193.76	8.644%	$210.5086	$210.51	$210.50	$210.50
Purchase #5	$38.91	8.394%	$42.1761	$42.18	$42.20	$42.20
Purchase #6	$216.67	9.700%	$237.687	$237.69	$237.70	$237.70
Purchase #7	$49.27	9.677%	$54.0379	$54.04	$54.05	$54.00
7 purchase totals =	$722.58		$793.5354	$793.55	$793.60	$793.50