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	$39.80	4.821%	$41.7188	$41.72	$41.70	$41.70
Purchase #2	$100.73	9.821%	$110.6227	$110.62	$110.60	$110.60
Purchase #3	$149.66	5.317%	$157.6174	$157.62	$157.60	$157.60
Purchase #4	$50.55	8.371%	$54.7815	$54.78	$54.80	$54.80
Purchase #5	$43.52	5.498%	$45.9127	$45.91	$45.90	$45.90
Purchase #6	$29.37	7.530%	$31.5816	$31.58	$31.60	$31.60
Purchase #7	$218.88	10.256%	$241.3283	$241.33	$241.35	$241.30
7 purchase totals =	$632.51		$683.5630	$683.56	$683.55	$683.50