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	$74.52	3.506%	$77.1327	$77.13	$77.15	$77.10
Purchase #2	$91.77	11.807%	$102.6053	$102.61	$102.60	$102.60
Purchase #3	$203.76	7.410%	$218.8586	$218.86	$218.85	$218.90
Purchase #4	$35.64	5.842%	$37.7221	$37.72	$37.70	$37.70
Purchase #5	$30.92	4.403%	$32.2814	$32.28	$32.30	$32.30
Purchase #6	$17.78	4.127%	$18.5138	$18.51	$18.50	$18.50
Purchase #7	$232.25	12.733%	$261.8224	$261.82	$261.80	$261.80
7 purchase totals =	$686.64		$748.9363	$748.93	$748.90	$748.90