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	$6.70	11.461%	$7.4679	$7.47	$7.45	$7.50
Purchase #2	$50.31	9.856%	$55.2686	$55.27	$55.25	$55.30
Purchase #3	$210.85	5.128%	$221.6624	$221.66	$221.65	$221.70
Purchase #4	$66.90	7.447%	$71.882	$71.88	$71.90	$71.90
Purchase #5	$62.26	9.632%	$68.2569	$68.26	$68.25	$68.30
Purchase #6	$65.84	5.445%	$69.425	$69.43	$69.45	$69.40
Purchase #7	$42.46	7.158%	$45.4993	$45.50	$45.50	$45.50
7 purchase totals =	$505.32		$539.4621	$539.47	$539.45	$539.60