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	$138.89	3.796%	$144.1623	$144.16	$144.15	$144.20
Purchase #2	$78.31	8.564%	$85.0165	$85.02	$85.00	$85.00
Purchase #3	$210.90	11.769%	$235.7208	$235.72	$235.70	$235.70
Purchase #4	$64.88	10.679%	$71.8085	$71.81	$71.80	$71.80
Purchase #5	$237.28	11.622%	$264.8567	$264.86	$264.85	$264.90
Purchase #6	$14.59	10.634%	$16.1415	$16.14	$16.15	$16.10
Purchase #7	$241.52	13.645%	$274.4754	$274.48	$274.50	$274.50
7 purchase totals =	$986.37		$1,092.1817	$1,092.19	$1,092.15	$1,092.20