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	$104.41	11.478%	$116.3942	$116.39	$116.40	$116.40
Purchase #2	$80.48	4.325%	$83.9608	$83.96	$83.95	$84.00
Purchase #3	$149.48	13.567%	$169.76	$169.76	$169.75	$169.80
Purchase #4	$8.70	13.702%	$9.8921	$9.89	$9.90	$9.90
Purchase #5	$34.87	6.779%	$37.2338	$37.23	$37.25	$37.20
Purchase #6	$146.43	5.546%	$154.551	$154.55	$154.55	$154.60
Purchase #7	$79.58	13.796%	$90.5589	$90.56	$90.55	$90.60
7 purchase totals =	$603.95		$662.3508	$662.34	$662.35	$662.50