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	$164.69	12.503%	$185.2812	$185.28	$185.30	$185.30
Purchase #2	$227.78	3.227%	$235.1305	$235.13	$235.15	$235.10
Purchase #3	$153.45	4.371%	$160.1573	$160.16	$160.15	$160.20
Purchase #4	$66.49	3.675%	$68.9335	$68.93	$68.95	$68.90
Purchase #5	$120.79	5.386%	$127.2957	$127.30	$127.30	$127.30
Purchase #6	$26.94	3.700%	$27.9368	$27.94	$27.95	$27.90
Purchase #7	$91.72	4.549%	$95.8923	$95.89	$95.90	$95.90
7 purchase totals =	$851.86		$900.6273	$900.63	$900.70	$900.60