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	$78.83	13.244%	$89.2702	$89.27	$89.25	$89.30
Purchase #2	$139.74	7.145%	$149.7244	$149.72	$149.70	$149.70
Purchase #3	$234.82	6.730%	$250.6234	$250.62	$250.60	$250.60
Purchase #4	$173.35	5.199%	$182.3625	$182.36	$182.35	$182.40
Purchase #5	$248.37	4.486%	$259.5119	$259.51	$259.50	$259.50
Purchase #6	$182.31	3.330%	$188.3809	$188.38	$188.40	$188.40
Purchase #7	$206.47	3.646%	$213.9979	$214.00	$214.00	$214.00
7 purchase totals =	$1,263.89		$1,333.8712	$1,333.86	$1,333.80	$1,333.90