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	$91.41	8.857%	$99.5062	$99.51	$99.50	$99.50
Purchase #2	$59.54	10.681%	$65.8995	$65.90	$65.90	$65.90
Purchase #3	$5.62	11.768%	$6.2814	$6.28	$6.30	$6.30
Purchase #4	$123.61	5.418%	$130.3072	$130.31	$130.30	$130.30
Purchase #5	$148.48	11.628%	$165.7453	$165.75	$165.75	$165.70
Purchase #6	$77.41	7.112%	$82.9154	$82.92	$82.90	$82.90
Purchase #7	$134.56	8.857%	$146.478	$146.48	$146.50	$146.50
7 purchase totals =	$640.63		$697.1330	$697.15	$697.15	$697.10