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	$5.69	12.782%	$6.4173	$6.42	$6.40	$6.40
Purchase #2	$215.69	4.166%	$224.6756	$224.68	$224.70	$224.70
Purchase #3	$79.33	8.267%	$85.8882	$85.89	$85.90	$85.90
Purchase #4	$28.97	5.622%	$30.5987	$30.60	$30.60	$30.60
Purchase #5	$63.34	13.434%	$71.8491	$71.85	$71.85	$71.80
Purchase #6	$33.69	5.556%	$35.5618	$35.56	$35.55	$35.60
Purchase #7	$108.92	8.798%	$118.5028	$118.50	$118.50	$118.50
7 purchase totals =	$535.63		$573.4935	$573.50	$573.50	$573.50