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	$18.93	7.417%	$20.334	$20.33	$20.35	$20.30
Purchase #2	$77.51	10.708%	$85.8098	$85.81	$85.80	$85.80
Purchase #3	$113.45	6.798%	$121.1623	$121.16	$121.15	$121.20
Purchase #4	$119.36	6.816%	$127.4956	$127.50	$127.50	$127.50
Purchase #5	$26.92	6.313%	$28.6195	$28.62	$28.60	$28.60
Purchase #6	$199.58	6.465%	$212.4828	$212.48	$212.50	$212.50
Purchase #7	$117.43	8.503%	$127.4151	$127.42	$127.40	$127.40
7 purchase totals =	$673.18		$723.3191	$723.32	$723.30	$723.30