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	$63.82	4.373%	$66.6108	$66.61	$66.60	$66.60
Purchase #2	$61.74	8.772%	$67.1558	$67.16	$67.15	$67.20
Purchase #3	$101.37	11.523%	$113.0509	$113.05	$113.05	$113.10
Purchase #4	$117.47	10.855%	$130.2214	$130.22	$130.20	$130.20
Purchase #5	$209.87	13.718%	$238.66	$238.66	$238.65	$238.70
Purchase #6	$82.53	11.301%	$91.8567	$91.86	$91.85	$91.90
Purchase #7	$144.86	7.738%	$156.0693	$156.07	$156.05	$156.10
7 purchase totals =	$781.66		$863.6249	$863.63	$863.55	$863.80