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	$127.89	6.717%	$136.4804	$136.48	$136.50	$136.50
Purchase #2	$71.86	7.794%	$77.4608	$77.46	$77.45	$77.50
Purchase #3	$162.53	3.333%	$167.9471	$167.95	$167.95	$167.90
Purchase #4	$134.56	6.480%	$143.2795	$143.28	$143.30	$143.30
Purchase #5	$222.86	13.540%	$253.0352	$253.04	$253.05	$253.00
Purchase #6	$60.27	6.761%	$64.3449	$64.34	$64.35	$64.30
Purchase #7	$55.44	5.468%	$58.4715	$58.47	$58.45	$58.50
7 purchase totals =	$835.41		$901.0194	$901.02	$901.05	$901.00