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	$90.36	10.179%	$99.5577	$99.56	$99.55	$99.60
Purchase #2	$11.82	4.465%	$12.3478	$12.35	$12.35	$12.30
Purchase #3	$19.86	7.396%	$21.3288	$21.33	$21.35	$21.30
Purchase #4	$198.42	13.323%	$224.8555	$224.86	$224.85	$224.90
Purchase #5	$170.90	7.776%	$184.1892	$184.19	$184.20	$184.20
Purchase #6	$200.47	11.675%	$223.8749	$223.87	$223.85	$223.90
Purchase #7	$12.85	11.310%	$14.3033	$14.30	$14.30	$14.30
7 purchase totals =	$704.68		$780.4572	$780.46	$780.45	$780.50