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	$188.84	5.159%	$198.5823	$198.58	$198.60	$198.60
Purchase #2	$55.90	7.680%	$60.1931	$60.19	$60.20	$60.20
Purchase #3	$88.35	13.729%	$100.4796	$100.48	$100.50	$100.50
Purchase #4	$20.56	8.355%	$22.2778	$22.28	$22.30	$22.30
Purchase #5	$143.46	6.372%	$152.6013	$152.60	$152.60	$152.60
Purchase #6	$152.56	3.574%	$158.0125	$158.01	$158.00	$158.00
Purchase #7	$158.89	4.410%	$165.897	$165.90	$165.90	$165.90
7 purchase totals =	$808.56		$858.0436	$858.04	$858.10	$858.10