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	$88.70	6.314%	$94.3005	$94.30	$94.30	$94.30
Purchase #2	$83.37	3.290%	$86.1129	$86.11	$86.10	$86.10
Purchase #3	$109.97	4.444%	$114.8571	$114.86	$114.85	$114.90
Purchase #4	$229.43	11.340%	$255.4474	$255.45	$255.45	$255.40
Purchase #5	$69.47	5.198%	$73.0811	$73.08	$73.10	$73.10
Purchase #6	$57.39	4.117%	$59.7527	$59.75	$59.75	$59.80
Purchase #7	$59.31	12.138%	$66.509	$66.51	$66.50	$66.50
7 purchase totals =	$697.64		$750.0607	$750.06	$750.05	$750.10