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	$129.56	6.343%	$137.778	$137.78	$137.80	$137.80
Purchase #2	$151.25	6.169%	$160.5806	$160.58	$160.60	$160.60
Purchase #3	$28.82	13.788%	$32.7937	$32.79	$32.80	$32.80
Purchase #4	$5.75	4.784%	$6.0251	$6.03	$6.05	$6.00
Purchase #5	$129.89	4.496%	$135.7299	$135.73	$135.75	$135.70
Purchase #6	$136.63	10.557%	$151.054	$151.05	$151.05	$151.10
Purchase #7	$40.63	5.465%	$42.8504	$42.85	$42.85	$42.90
7 purchase totals =	$622.53		$666.8117	$666.81	$666.90	$666.90