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	$180.95	4.229%	$188.6024	$188.60	$188.60	$188.60
Purchase #2	$129.74	13.270%	$146.9565	$146.96	$146.95	$147.00
Purchase #3	$160.61	9.486%	$175.8455	$175.85	$175.85	$175.80
Purchase #4	$5.88	10.628%	$6.5049	$6.50	$6.50	$6.50
Purchase #5	$85.61	6.386%	$91.0771	$91.08	$91.10	$91.10
Purchase #6	$165.59	11.733%	$185.0187	$185.02	$185.00	$185.00
Purchase #7	$52.43	13.245%	$59.3744	$59.37	$59.35	$59.40
7 purchase totals =	$780.81		$853.3795	$853.38	$853.35	$853.40