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	$55.88	7.658%	$60.1593	$60.16	$60.15	$60.20
Purchase #2	$35.90	3.477%	$37.1482	$37.15	$37.15	$37.10
Purchase #3	$188.95	12.764%	$213.0676	$213.07	$213.05	$213.10
Purchase #4	$15.86	10.408%	$17.5107	$17.51	$17.50	$17.50
Purchase #5	$7.78	10.432%	$8.5916	$8.59	$8.60	$8.60
Purchase #6	$135.34	5.302%	$142.5157	$142.52	$142.50	$142.50
Purchase #7	$26.80	5.624%	$28.3072	$28.31	$28.30	$28.30
7 purchase totals =	$466.51		$507.3003	$507.31	$507.25	$507.30