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	$234.74	10.297%	$258.9112	$258.91	$258.90	$258.90
Purchase #2	$18.51	3.454%	$19.1493	$19.15	$19.15	$19.10
Purchase #3	$83.36	5.794%	$88.1899	$88.19	$88.20	$88.20
Purchase #4	$64.88	9.631%	$71.1286	$71.13	$71.15	$71.10
Purchase #5	$99.30	10.606%	$109.8318	$109.83	$109.85	$109.80
Purchase #6	$18.56	13.352%	$21.0381	$21.04	$21.05	$21.00
Purchase #7	$209.53	9.102%	$228.6014	$228.60	$228.60	$228.60
7 purchase totals =	$728.88		$796.8503	$796.85	$796.90	$796.70