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	$81.43	6.587%	$86.7938	$86.79	$86.80	$86.80
Purchase #2	$152.48	12.323%	$171.2701	$171.27	$171.25	$171.30
Purchase #3	$32.53	5.150%	$34.2053	$34.21	$34.20	$34.20
Purchase #4	$104.70	6.123%	$111.1108	$111.11	$111.10	$111.10
Purchase #5	$21.95	5.799%	$23.2229	$23.22	$23.20	$23.20
Purchase #6	$80.42	11.754%	$89.8726	$89.87	$89.85	$89.90
Purchase #7	$10.80	11.507%	$12.0428	$12.04	$12.05	$12.00
7 purchase totals =	$484.31		$528.5183	$528.51	$528.45	$528.50