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	$165.88	13.245%	$187.8508	$187.85	$187.85	$187.90
Purchase #2	$102.59	10.737%	$113.6051	$113.61	$113.60	$113.60
Purchase #3	$84.40	7.762%	$90.9511	$90.95	$90.95	$91.00
Purchase #4	$101.87	3.460%	$105.3947	$105.39	$105.40	$105.40
Purchase #5	$110.64	8.828%	$120.4073	$120.41	$120.40	$120.40
Purchase #6	$22.25	11.320%	$24.7687	$24.77	$24.75	$24.80
Purchase #7	$25.25	11.500%	$28.1538	$28.15	$28.15	$28.20
7 purchase totals =	$612.88		$671.1315	$671.13	$671.10	$671.30