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	$31.87	6.289%	$33.8743	$33.87	$33.85	$33.90
Purchase #2	$131.55	11.527%	$146.7138	$146.71	$146.70	$146.70
Purchase #3	$229.83	3.107%	$236.9708	$236.97	$236.95	$237.00
Purchase #4	$62.31	4.148%	$64.8946	$64.89	$64.90	$64.90
Purchase #5	$74.96	10.358%	$82.7244	$82.72	$82.70	$82.70
Purchase #6	$44.40	13.786%	$50.521	$50.52	$50.50	$50.50
Purchase #7	$172.79	9.370%	$188.9804	$188.98	$189.00	$189.00
7 purchase totals =	$747.71		$804.6793	$804.66	$804.60	$804.70