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	$138.88	8.445%	$150.6084	$150.61	$150.60	$150.60
Purchase #2	$243.88	9.168%	$266.2389	$266.24	$266.25	$266.20
Purchase #3	$20.28	5.813%	$21.4589	$21.46	$21.45	$21.50
Purchase #4	$50.61	10.458%	$55.9028	$55.90	$55.90	$55.90
Purchase #5	$6.83	4.137%	$7.1126	$7.11	$7.10	$7.10
Purchase #6	$200.32	10.356%	$221.0651	$221.07	$221.05	$221.10
Purchase #7	$244.38	7.713%	$263.229	$263.23	$263.25	$263.20
7 purchase totals =	$905.18		$985.6157	$985.62	$985.60	$985.60