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	$205.39	6.579%	$218.9026	$218.90	$218.90	$218.90
Purchase #2	$240.42	7.569%	$258.6174	$258.62	$258.60	$258.60
Purchase #3	$151.60	12.663%	$170.7971	$170.80	$170.80	$170.80
Purchase #4	$240.56	11.480%	$268.1763	$268.18	$268.20	$268.20
Purchase #5	$145.65	9.383%	$159.3163	$159.32	$159.30	$159.30
Purchase #6	$55.82	6.554%	$59.4784	$59.48	$59.50	$59.50
Purchase #7	$212.73	4.464%	$222.2263	$222.23	$222.25	$222.20
7 purchase totals =	$1,252.17		$1,357.5144	$1,357.53	$1,357.55	$1,357.50