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	$249.86	8.607%	$271.3655	$271.37	$271.35	$271.40
Purchase #2	$116.31	3.283%	$120.1285	$120.13	$120.15	$120.10
Purchase #3	$57.88	13.295%	$65.5751	$65.58	$65.60	$65.60
Purchase #4	$179.98	10.712%	$199.2595	$199.26	$199.25	$199.30
Purchase #5	$245.77	11.325%	$273.6035	$273.60	$273.60	$273.60
Purchase #6	$72.82	7.251%	$78.1002	$78.10	$78.10	$78.10
Purchase #7	$87.61	6.575%	$93.3704	$93.37	$93.35	$93.40
7 purchase totals =	$1,010.23		$1,101.4027	$1,101.41	$1,101.40	$1,101.50