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	$21.41	4.377%	$22.3471	$22.35	$22.35	$22.30
Purchase #2	$83.94	6.161%	$89.1115	$89.11	$89.10	$89.10
Purchase #3	$77.45	10.604%	$85.6628	$85.66	$85.65	$85.70
Purchase #4	$11.30	13.767%	$12.8557	$12.86	$12.85	$12.90
Purchase #5	$72.63	11.376%	$80.8924	$80.89	$80.90	$80.90
Purchase #6	$37.52	9.715%	$41.1651	$41.17	$41.15	$41.20
Purchase #7	$86.29	6.624%	$92.0058	$92.01	$92.00	$92.00
7 purchase totals =	$390.54		$424.0404	$424.05	$424.00	$424.10