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	$166.37	3.859%	$172.7902	$172.79	$172.80	$172.80
Purchase #2	$123.72	10.674%	$136.9259	$136.93	$136.95	$136.90
Purchase #3	$214.33	11.444%	$238.8579	$238.86	$238.85	$238.90
Purchase #4	$187.55	12.817%	$211.5883	$211.59	$211.60	$211.60
Purchase #5	$239.98	13.867%	$273.258	$273.26	$273.25	$273.30
Purchase #6	$141.72	11.173%	$157.5544	$157.55	$157.55	$157.60
Purchase #7	$63.85	11.494%	$71.1889	$71.19	$71.20	$71.20
7 purchase totals =	$1,137.52		$1,262.1636	$1,262.17	$1,262.20	$1,262.30