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	$64.67	11.161%	$71.8878	$71.89	$71.90	$71.90
Purchase #2	$150.71	6.472%	$160.464	$160.46	$160.45	$160.50
Purchase #3	$94.45	5.784%	$99.913	$99.91	$99.90	$99.90
Purchase #4	$194.74	13.613%	$221.25	$221.25	$221.25	$221.30
Purchase #5	$158.41	13.454%	$179.7225	$179.72	$179.70	$179.70
Purchase #6	$245.98	9.842%	$270.1894	$270.19	$270.20	$270.20
Purchase #7	$62.55	12.184%	$70.1711	$70.17	$70.15	$70.20
7 purchase totals =	$971.51		$1,073.5978	$1,073.59	$1,073.55	$1,073.70