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	$209.96	6.458%	$223.5192	$223.52	$223.50	$223.50
Purchase #2	$110.31	11.537%	$123.0365	$123.04	$123.05	$123.00
Purchase #3	$26.53	8.660%	$28.8275	$28.83	$28.85	$28.80
Purchase #4	$97.87	7.448%	$105.1594	$105.16	$105.15	$105.20
Purchase #5	$204.29	12.330%	$229.479	$229.48	$229.50	$229.50
Purchase #6	$141.34	3.869%	$146.8084	$146.81	$146.80	$146.80
Purchase #7	$204.81	8.582%	$222.3868	$222.39	$222.40	$222.40
7 purchase totals =	$995.11		$1,079.2168	$1,079.23	$1,079.25	$1,079.20