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	$138.45	8.484%	$150.1961	$150.20	$150.20	$150.20
Purchase #2	$192.87	12.215%	$216.4291	$216.43	$216.45	$216.40
Purchase #3	$83.30	11.739%	$93.0786	$93.08	$93.10	$93.10
Purchase #4	$188.59	6.259%	$200.3938	$200.39	$200.40	$200.40
Purchase #5	$82.41	11.308%	$91.7289	$91.73	$91.75	$91.70
Purchase #6	$102.26	11.331%	$113.8471	$113.85	$113.85	$113.80
Purchase #7	$79.90	13.796%	$90.923	$90.92	$90.90	$90.90
7 purchase totals =	$867.78		$956.5966	$956.60	$956.65	$956.50