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	$53.43	11.321%	$59.4788	$59.48	$59.50	$59.50
Purchase #2	$66.30	8.150%	$71.7035	$71.70	$71.70	$71.70
Purchase #3	$120.77	7.183%	$129.4449	$129.44	$129.45	$129.40
Purchase #4	$231.99	9.430%	$253.8667	$253.87	$253.85	$253.90
Purchase #5	$174.53	13.724%	$198.4825	$198.48	$198.50	$198.50
Purchase #6	$77.48	3.763%	$80.3956	$80.40	$80.40	$80.40
Purchase #7	$127.59	7.290%	$136.8913	$136.89	$136.90	$136.90
7 purchase totals =	$852.09		$930.2633	$930.26	$930.30	$930.30