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	$45.79	6.781%	$48.895	$48.90	$48.90	$48.90
Purchase #2	$96.34	5.795%	$101.9229	$101.92	$101.90	$101.90
Purchase #3	$39.26	3.198%	$40.5155	$40.52	$40.50	$40.50
Purchase #4	$42.84	4.666%	$44.8389	$44.84	$44.85	$44.80
Purchase #5	$135.78	7.587%	$146.0816	$146.08	$146.10	$146.10
Purchase #6	$172.36	4.592%	$180.2748	$180.27	$180.25	$180.30
Purchase #7	$221.72	5.331%	$233.5399	$233.54	$233.55	$233.50
7 purchase totals =	$754.09		$796.0686	$796.07	$796.05	$796.00