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	$6.72	12.641%	$7.5695	$7.57	$7.55	$7.60
Purchase #2	$165.83	5.785%	$175.4233	$175.42	$175.40	$175.40
Purchase #3	$199.96	10.222%	$220.3999	$220.40	$220.40	$220.40
Purchase #4	$194.81	12.350%	$218.869	$218.87	$218.85	$218.90
Purchase #5	$165.48	13.686%	$188.1276	$188.13	$188.15	$188.10
Purchase #6	$150.73	3.327%	$155.7448	$155.74	$155.75	$155.70
Purchase #7	$40.89	6.196%	$43.4235	$43.42	$43.40	$43.40
7 purchase totals =	$924.42		$1,009.5576	$1,009.55	$1,009.50	$1,009.50