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	$134.48	5.198%	$141.4703	$141.47	$141.45	$141.50
Purchase #2	$34.72	6.618%	$37.0178	$37.02	$37.00	$37.00
Purchase #3	$173.72	10.345%	$191.6913	$191.69	$191.70	$191.70
Purchase #4	$95.52	4.482%	$99.8012	$99.80	$99.80	$99.80
Purchase #5	$229.97	4.511%	$240.3439	$240.34	$240.35	$240.30
Purchase #6	$51.61	7.141%	$55.2955	$55.30	$55.30	$55.30
Purchase #7	$72.44	5.111%	$76.1424	$76.14	$76.15	$76.10
7 purchase totals =	$792.46		$841.7624	$841.76	$841.75	$841.70