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	$237.52	13.309%	$269.1315	$269.13	$269.15	$269.10
Purchase #2	$161.57	6.814%	$172.5794	$172.58	$172.60	$172.60
Purchase #3	$85.79	7.773%	$92.4585	$92.46	$92.45	$92.50
Purchase #4	$123.40	13.166%	$139.6468	$139.65	$139.65	$139.60
Purchase #5	$250.39	13.395%	$283.9297	$283.93	$283.95	$283.90
Purchase #6	$36.47	3.160%	$37.6225	$37.62	$37.60	$37.60
Purchase #7	$90.35	6.129%	$95.8876	$95.89	$95.90	$95.90
7 purchase totals =	$985.49		$1,091.2560	$1,091.26	$1,091.30	$1,091.20