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	$80.26	3.521%	$83.086	$83.09	$83.10	$83.10
Purchase #2	$31.97	12.363%	$35.9225	$35.92	$35.90	$35.90
Purchase #3	$23.79	5.808%	$25.1717	$25.17	$25.15	$25.20
Purchase #4	$79.32	4.361%	$82.7791	$82.78	$82.80	$82.80
Purchase #5	$154.43	13.821%	$175.7738	$175.77	$175.75	$175.80
Purchase #6	$32.27	5.140%	$33.9287	$33.93	$33.95	$33.90
Purchase #7	$28.86	12.625%	$32.5036	$32.50	$32.50	$32.50
7 purchase totals =	$430.90		$469.1654	$469.16	$469.15	$469.20