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	$38.71	9.173%	$42.2609	$42.26	$42.25	$42.30
Purchase #2	$144.58	11.154%	$160.7065	$160.71	$160.70	$160.70
Purchase #3	$94.29	7.476%	$101.3391	$101.34	$101.35	$101.30
Purchase #4	$37.38	10.527%	$41.315	$41.32	$41.30	$41.30
Purchase #5	$36.25	6.441%	$38.5849	$38.58	$38.60	$38.60
Purchase #6	$99.28	12.378%	$111.5689	$111.57	$111.55	$111.60
Purchase #7	$17.48	12.740%	$19.707	$19.71	$19.70	$19.70
7 purchase totals =	$467.97		$515.4823	$515.49	$515.45	$515.50