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	$7.50	3.804%	$7.7853	$7.79	$7.80	$7.80
Purchase #2	$160.88	7.239%	$172.5261	$172.53	$172.55	$172.50
Purchase #3	$182.89	11.552%	$204.0175	$204.02	$204.00	$204.00
Purchase #4	$34.59	11.320%	$38.5056	$38.51	$38.50	$38.50
Purchase #5	$140.64	4.812%	$147.4076	$147.41	$147.40	$147.40
Purchase #6	$59.73	4.350%	$62.3283	$62.33	$62.35	$62.30
Purchase #7	$242.53	13.175%	$274.4833	$274.48	$274.50	$274.50
7 purchase totals =	$828.76		$907.0537	$907.07	$907.10	$907.00