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	$37.58	6.192%	$39.907	$39.91	$39.90	$39.90
Purchase #2	$149.66	3.691%	$155.184	$155.18	$155.20	$155.20
Purchase #3	$80.93	11.670%	$90.3745	$90.37	$90.35	$90.40
Purchase #4	$165.37	9.250%	$180.6667	$180.67	$180.65	$180.70
Purchase #5	$77.89	8.327%	$84.3759	$84.38	$84.40	$84.40
Purchase #6	$10.64	5.535%	$11.2289	$11.23	$11.25	$11.20
Purchase #7	$233.50	13.313%	$264.5859	$264.59	$264.60	$264.60
7 purchase totals =	$755.57		$826.3229	$826.33	$826.35	$826.40