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	$121.95	12.729%	$137.473	$137.47	$137.45	$137.50
Purchase #2	$23.31	12.234%	$26.1617	$26.16	$26.15	$26.20
Purchase #3	$184.91	8.362%	$200.3722	$200.37	$200.35	$200.40
Purchase #4	$100.72	6.126%	$106.8901	$106.89	$106.90	$106.90
Purchase #5	$166.36	3.544%	$172.2558	$172.26	$172.25	$172.30
Purchase #6	$62.73	6.642%	$66.8965	$66.90	$66.90	$66.90
Purchase #7	$48.29	6.111%	$51.241	$51.24	$51.25	$51.20
7 purchase totals =	$708.27		$761.2903	$761.29	$761.25	$761.40