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	$158.65	7.587%	$170.6868	$170.69	$170.70	$170.70
Purchase #2	$58.95	6.349%	$62.6927	$62.69	$62.70	$62.70
Purchase #3	$62.78	7.868%	$67.7195	$67.72	$67.70	$67.70
Purchase #4	$170.31	12.292%	$191.2445	$191.24	$191.25	$191.20
Purchase #5	$53.28	12.401%	$59.8873	$59.89	$59.90	$59.90
Purchase #6	$220.89	10.330%	$243.7079	$243.71	$243.70	$243.70
Purchase #7	$30.68	13.563%	$34.8411	$34.84	$34.85	$34.80
7 purchase totals =	$755.54		$830.7798	$830.78	$830.80	$830.70