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	$122.35	7.652%	$131.7122	$131.71	$131.70	$131.70
Purchase #2	$223.30	12.292%	$250.748	$250.75	$250.75	$250.70
Purchase #3	$90.78	12.594%	$102.2128	$102.21	$102.20	$102.20
Purchase #4	$113.30	5.858%	$119.9371	$119.94	$119.95	$119.90
Purchase #5	$188.65	13.162%	$213.4801	$213.48	$213.50	$213.50
Purchase #6	$85.40	5.488%	$90.0868	$90.09	$90.10	$90.10
Purchase #7	$54.85	7.860%	$59.1612	$59.16	$59.15	$59.20
7 purchase totals =	$878.63		$967.3382	$967.34	$967.35	$967.30