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	$130.61	7.305%	$140.1511	$140.15	$140.15	$140.20
Purchase #2	$78.57	10.420%	$86.757	$86.76	$86.75	$86.80
Purchase #3	$20.79	10.394%	$22.9509	$22.95	$22.95	$23.00
Purchase #4	$51.73	10.400%	$57.1099	$57.11	$57.10	$57.10
Purchase #5	$131.92	6.333%	$140.2745	$140.27	$140.25	$140.30
Purchase #6	$68.57	7.211%	$73.5146	$73.51	$73.50	$73.50
Purchase #7	$89.92	11.371%	$100.1448	$100.14	$100.15	$100.10
7 purchase totals =	$572.11		$620.9028	$620.89	$620.85	$621.00