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	$91.81	11.809%	$102.6518	$102.65	$102.65	$102.70
Purchase #2	$89.61	11.749%	$100.1383	$100.14	$100.15	$100.10
Purchase #3	$77.77	12.233%	$87.2836	$87.28	$87.30	$87.30
Purchase #4	$198.35	10.195%	$218.5718	$218.57	$218.55	$218.60
Purchase #5	$10.36	11.173%	$11.5175	$11.52	$11.50	$11.50
Purchase #6	$74.28	11.321%	$82.6892	$82.69	$82.70	$82.70
Purchase #7	$216.62	9.231%	$236.6162	$236.62	$236.60	$236.60
7 purchase totals =	$758.80		$839.4684	$839.47	$839.45	$839.50