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	$88.51	13.799%	$100.7235	$100.72	$100.70	$100.70
Purchase #2	$91.40	8.253%	$98.9432	$98.94	$98.95	$98.90
Purchase #3	$134.70	9.524%	$147.5288	$147.53	$147.55	$147.50
Purchase #4	$72.65	6.348%	$77.2618	$77.26	$77.25	$77.30
Purchase #5	$32.43	6.459%	$34.5247	$34.52	$34.50	$34.50
Purchase #6	$56.25	9.537%	$61.6146	$61.61	$61.60	$61.60
Purchase #7	$9.96	3.520%	$10.3106	$10.31	$10.30	$10.30
7 purchase totals =	$485.90		$530.9072	$530.89	$530.85	$530.80