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	$101.51	11.562%	$113.2466	$113.25	$113.25	$113.20
Purchase #2	$111.30	6.325%	$118.3397	$118.34	$118.35	$118.30
Purchase #3	$109.33	13.671%	$124.2765	$124.28	$124.30	$124.30
Purchase #4	$168.54	13.261%	$190.8901	$190.89	$190.90	$190.90
Purchase #5	$8.87	4.285%	$9.2501	$9.25	$9.25	$9.30
Purchase #6	$84.88	6.602%	$90.4838	$90.48	$90.50	$90.50
Purchase #7	$82.76	13.702%	$94.0998	$94.10	$94.10	$94.10
7 purchase totals =	$667.19		$740.5866	$740.59	$740.65	$740.60