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	$175.27	13.541%	$199.0033	$199.00	$199.00	$199.00
Purchase #2	$156.84	6.702%	$167.3514	$167.35	$167.35	$167.40
Purchase #3	$69.45	11.663%	$77.55	$77.55	$77.55	$77.60
Purchase #4	$130.41	10.211%	$143.7262	$143.73	$143.75	$143.70
Purchase #5	$38.72	3.776%	$40.1821	$40.18	$40.20	$40.20
Purchase #6	$96.28	5.300%	$101.3828	$101.38	$101.40	$101.40
Purchase #7	$80.34	13.394%	$91.1007	$91.10	$91.10	$91.10
7 purchase totals =	$747.31		$820.2965	$820.29	$820.35	$820.40