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	$89.73	11.343%	$99.9081	$99.91	$99.90	$99.90
Purchase #2	$55.71	7.698%	$59.9986	$60.00	$60.00	$60.00
Purchase #3	$175.62	7.173%	$188.2172	$188.22	$188.20	$188.20
Purchase #4	$247.71	10.538%	$273.8137	$273.81	$273.80	$273.80
Purchase #5	$215.96	3.132%	$222.7239	$222.72	$222.70	$222.70
Purchase #6	$227.42	9.645%	$249.3547	$249.35	$249.35	$249.40
Purchase #7	$160.27	13.378%	$181.7109	$181.71	$181.70	$181.70
7 purchase totals =	$1,172.42		$1,275.7271	$1,275.72	$1,275.65	$1,275.70