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	$246.26	11.866%	$275.4812	$275.48	$275.50	$275.50
Purchase #2	$84.49	6.412%	$89.9075	$89.91	$89.90	$89.90
Purchase #3	$138.83	6.392%	$147.704	$147.70	$147.70	$147.70
Purchase #4	$109.42	9.178%	$119.4626	$119.46	$119.45	$119.50
Purchase #5	$141.52	5.626%	$149.4819	$149.48	$149.50	$149.50
Purchase #6	$238.79	11.696%	$266.7189	$266.72	$266.70	$266.70
Purchase #7	$79.92	3.781%	$82.9418	$82.94	$82.95	$82.90
7 purchase totals =	$1,039.23		$1,131.6979	$1,131.69	$1,131.70	$1,131.70