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	$188.55	6.244%	$200.3231	$200.32	$200.30	$200.30
Purchase #2	$218.35	13.359%	$247.5194	$247.52	$247.50	$247.50
Purchase #3	$145.69	7.672%	$156.8673	$156.87	$156.85	$156.90
Purchase #4	$59.57	7.809%	$64.2218	$64.22	$64.20	$64.20
Purchase #5	$49.35	7.714%	$53.1569	$53.16	$53.15	$53.20
Purchase #6	$237.60	7.287%	$254.9139	$254.91	$254.90	$254.90
Purchase #7	$249.27	9.559%	$273.0977	$273.10	$273.10	$273.10
7 purchase totals =	$1,148.38		$1,250.1001	$1,250.10	$1,250.00	$1,250.10