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	$25.48	13.196%	$28.8423	$28.84	$28.85	$28.80
Purchase #2	$199.61	12.426%	$224.4135	$224.41	$224.40	$224.40
Purchase #3	$32.72	13.309%	$37.0747	$37.07	$37.05	$37.10
Purchase #4	$105.43	10.342%	$116.3336	$116.33	$116.35	$116.30
Purchase #5	$150.62	13.661%	$171.1962	$171.20	$171.20	$171.20
Purchase #6	$179.93	4.485%	$187.9999	$188.00	$188.00	$188.00
Purchase #7	$61.64	11.573%	$68.7736	$68.77	$68.75	$68.80
7 purchase totals =	$755.43		$834.6338	$834.62	$834.60	$834.60