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	$117.98	8.696%	$128.2395	$128.24	$128.25	$128.20
Purchase #2	$136.56	3.406%	$141.2112	$141.21	$141.20	$141.20
Purchase #3	$172.56	11.290%	$192.042	$192.04	$192.05	$192.00
Purchase #4	$32.35	13.702%	$36.7826	$36.78	$36.80	$36.80
Purchase #5	$45.31	6.505%	$48.2574	$48.26	$48.25	$48.30
Purchase #6	$38.83	10.469%	$42.8951	$42.90	$42.90	$42.90
Purchase #7	$72.67	7.636%	$78.2191	$78.22	$78.20	$78.20
7 purchase totals =	$616.26		$667.6469	$667.65	$667.65	$667.60