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	$65.51	12.251%	$73.5356	$73.54	$73.55	$73.50
Purchase #2	$196.70	12.441%	$221.1714	$221.17	$221.15	$221.20
Purchase #3	$67.40	6.483%	$71.7695	$71.77	$71.75	$71.80
Purchase #4	$43.90	4.539%	$45.8926	$45.89	$45.90	$45.90
Purchase #5	$241.93	4.656%	$253.1943	$253.19	$253.20	$253.20
Purchase #6	$18.71	8.306%	$20.2641	$20.26	$20.25	$20.30
Purchase #7	$58.91	11.490%	$65.6788	$65.68	$65.70	$65.70
7 purchase totals =	$693.06		$751.5063	$751.50	$751.50	$751.60