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	$144.90	9.390%	$158.5061	$158.51	$158.50	$158.50
Purchase #2	$115.47	11.762%	$129.0516	$129.05	$129.05	$129.10
Purchase #3	$144.28	9.217%	$157.5783	$157.58	$157.60	$157.60
Purchase #4	$147.56	6.288%	$156.8386	$156.84	$156.85	$156.80
Purchase #5	$52.50	4.836%	$55.0389	$55.04	$55.05	$55.00
Purchase #6	$90.70	9.686%	$99.4852	$99.49	$99.50	$99.50
Purchase #7	$63.28	13.760%	$71.9873	$71.99	$72.00	$72.00
7 purchase totals =	$758.69		$828.4860	$828.50	$828.55	$828.50