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	$222.60	13.712%	$253.1229	$253.12	$253.10	$253.10
Purchase #2	$142.68	12.475%	$160.4793	$160.48	$160.50	$160.50
Purchase #3	$82.39	5.788%	$87.1587	$87.16	$87.15	$87.20
Purchase #4	$64.56	9.725%	$70.8385	$70.84	$70.85	$70.80
Purchase #5	$116.89	11.800%	$130.683	$130.68	$130.70	$130.70
Purchase #6	$165.72	9.143%	$180.8718	$180.87	$180.85	$180.90
Purchase #7	$88.30	7.778%	$95.168	$95.17	$95.15	$95.20
7 purchase totals =	$883.14		$978.3222	$978.32	$978.30	$978.40