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	$128.49	6.254%	$136.5258	$136.53	$136.55	$136.50
Purchase #2	$91.96	10.171%	$101.3133	$101.31	$101.30	$101.30
Purchase #3	$240.62	10.408%	$265.6637	$265.66	$265.65	$265.70
Purchase #4	$38.66	10.811%	$42.8395	$42.84	$42.85	$42.80
Purchase #5	$48.89	9.863%	$53.712	$53.71	$53.70	$53.70
Purchase #6	$173.38	5.248%	$182.479	$182.48	$182.50	$182.50
Purchase #7	$45.31	10.269%	$49.9629	$49.96	$49.95	$50.00
7 purchase totals =	$767.31		$832.4962	$832.49	$832.50	$832.50