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	$120.42	11.206%	$133.9143	$133.91	$133.90	$133.90
Purchase #2	$155.54	6.650%	$165.8834	$165.88	$165.90	$165.90
Purchase #3	$75.49	9.160%	$82.4049	$82.40	$82.40	$82.40
Purchase #4	$243.33	8.802%	$264.7479	$264.75	$264.75	$264.70
Purchase #5	$44.38	6.344%	$47.1955	$47.20	$47.20	$47.20
Purchase #6	$222.81	8.423%	$241.5773	$241.58	$241.60	$241.60
Purchase #7	$49.48	10.208%	$54.5309	$54.53	$54.55	$54.50
7 purchase totals =	$911.45		$990.2542	$990.25	$990.30	$990.20