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	$152.36	13.578%	$173.0474	$173.05	$173.05	$173.00
Purchase #2	$55.56	11.816%	$62.125	$62.13	$62.15	$62.10
Purchase #3	$101.54	10.789%	$112.4952	$112.50	$112.50	$112.50
Purchase #4	$109.47	13.694%	$124.4608	$124.46	$124.45	$124.50
Purchase #5	$128.80	8.796%	$140.1292	$140.13	$140.15	$140.10
Purchase #6	$119.45	10.169%	$131.5969	$131.60	$131.60	$131.60
Purchase #7	$159.26	11.429%	$177.4618	$177.46	$177.45	$177.50
7 purchase totals =	$826.44		$921.3163	$921.33	$921.35	$921.30