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	$170.42	10.742%	$188.7265	$188.73	$188.75	$188.70
Purchase #2	$49.31	8.632%	$53.5664	$53.57	$53.55	$53.60
Purchase #3	$206.93	11.433%	$230.5883	$230.59	$230.60	$230.60
Purchase #4	$190.67	4.611%	$199.4618	$199.46	$199.45	$199.50
Purchase #5	$203.28	8.342%	$220.2376	$220.24	$220.25	$220.20
Purchase #6	$193.43	3.474%	$200.1498	$200.15	$200.15	$200.10
Purchase #7	$172.37	13.798%	$196.1536	$196.15	$196.15	$196.20
7 purchase totals =	$1,186.41		$1,288.8840	$1,288.89	$1,288.90	$1,288.90