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	$148.86	4.143%	$155.0273	$155.03	$155.05	$155.00
Purchase #2	$86.60	13.540%	$98.3256	$98.33	$98.35	$98.30
Purchase #3	$111.44	11.610%	$124.3782	$124.38	$124.40	$124.40
Purchase #4	$132.76	10.507%	$146.7091	$146.71	$146.70	$146.70
Purchase #5	$91.38	7.269%	$98.0224	$98.02	$98.00	$98.00
Purchase #6	$28.91	13.855%	$32.9155	$32.92	$32.90	$32.90
Purchase #7	$130.74	10.226%	$144.1095	$144.11	$144.10	$144.10
7 purchase totals =	$730.69		$799.4876	$799.50	$799.50	$799.40