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	$36.78	10.318%	$40.575	$40.58	$40.60	$40.60
Purchase #2	$95.43	3.662%	$98.9246	$98.92	$98.90	$98.90
Purchase #3	$186.44	13.257%	$211.1564	$211.16	$211.15	$211.20
Purchase #4	$70.41	11.581%	$78.5642	$78.56	$78.55	$78.60
Purchase #5	$84.31	7.258%	$90.4292	$90.43	$90.45	$90.40
Purchase #6	$212.29	5.450%	$223.8598	$223.86	$223.85	$223.90
Purchase #7	$235.62	3.816%	$244.6113	$244.61	$244.60	$244.60
7 purchase totals =	$921.28		$988.1205	$988.12	$988.10	$988.20