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	$34.95	9.133%	$38.142	$38.14	$38.15	$38.10
Purchase #2	$19.32	3.569%	$20.0095	$20.01	$20.00	$20.00
Purchase #3	$70.60	10.137%	$77.7567	$77.76	$77.75	$77.80
Purchase #4	$209.56	13.805%	$238.4898	$238.49	$238.50	$238.50
Purchase #5	$82.75	10.317%	$91.2873	$91.29	$91.30	$91.30
Purchase #6	$245.44	12.142%	$275.2413	$275.24	$275.25	$275.20
Purchase #7	$30.64	5.543%	$32.3384	$32.34	$32.35	$32.30
7 purchase totals =	$693.26		$773.2650	$773.27	$773.30	$773.20