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	$144.45	11.707%	$161.3608	$161.36	$161.35	$161.40
Purchase #2	$110.60	10.172%	$121.8502	$121.85	$121.85	$121.90
Purchase #3	$230.87	10.374%	$254.8205	$254.82	$254.80	$254.80
Purchase #4	$203.61	4.475%	$212.7215	$212.72	$212.70	$212.70
Purchase #5	$152.44	10.294%	$168.1322	$168.13	$168.15	$168.10
Purchase #6	$37.31	12.854%	$42.1058	$42.11	$42.10	$42.10
Purchase #7	$147.93	5.139%	$155.5321	$155.53	$155.55	$155.50
7 purchase totals =	$1,027.21		$1,116.5231	$1,116.52	$1,116.50	$1,116.50