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	$104.96	6.444%	$111.7236	$111.72	$111.70	$111.70
Purchase #2	$51.60	12.649%	$58.1269	$58.13	$58.15	$58.10
Purchase #3	$141.36	7.645%	$152.167	$152.17	$152.15	$152.20
Purchase #4	$34.82	9.538%	$38.1411	$38.14	$38.15	$38.10
Purchase #5	$101.75	7.600%	$109.483	$109.48	$109.50	$109.50
Purchase #6	$139.96	13.651%	$159.0659	$159.07	$159.05	$159.10
Purchase #7	$13.76	12.653%	$15.5011	$15.50	$15.50	$15.50
7 purchase totals =	$588.21		$644.2086	$644.21	$644.20	$644.20