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	$31.43	6.188%	$33.3749	$33.37	$33.35	$33.40
Purchase #2	$205.99	7.474%	$221.3857	$221.39	$221.40	$221.40
Purchase #3	$135.85	11.565%	$151.5611	$151.56	$151.55	$151.60
Purchase #4	$152.81	8.229%	$165.3847	$165.38	$165.40	$165.40
Purchase #5	$32.52	8.229%	$35.1961	$35.20	$35.20	$35.20
Purchase #6	$87.49	3.336%	$90.4087	$90.41	$90.40	$90.40
Purchase #7	$102.61	10.640%	$113.5277	$113.53	$113.55	$113.50
7 purchase totals =	$748.70		$810.8389	$810.84	$810.85	$810.90