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	$116.77	11.833%	$130.5874	$130.59	$130.60	$130.60
Purchase #2	$194.25	4.801%	$203.5759	$203.58	$203.60	$203.60
Purchase #3	$125.75	11.773%	$140.5545	$140.55	$140.55	$140.60
Purchase #4	$200.56	9.282%	$219.176	$219.18	$219.20	$219.20
Purchase #5	$84.37	6.344%	$89.7224	$89.72	$89.70	$89.70
Purchase #6	$136.50	11.754%	$152.5442	$152.54	$152.55	$152.50
Purchase #7	$49.58	12.784%	$55.9183	$55.92	$55.90	$55.90
7 purchase totals =	$907.78		$992.0787	$992.08	$992.10	$992.10