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	$203.82	7.797%	$219.7118	$219.71	$219.70	$219.70
Purchase #2	$138.32	5.526%	$145.9636	$145.96	$145.95	$146.00
Purchase #3	$219.72	12.677%	$247.5739	$247.57	$247.55	$247.60
Purchase #4	$170.38	7.277%	$182.7786	$182.78	$182.80	$182.80
Purchase #5	$73.40	13.600%	$83.3824	$83.38	$83.40	$83.40
Purchase #6	$40.38	12.208%	$45.3096	$45.31	$45.30	$45.30
Purchase #7	$97.36	8.708%	$105.8381	$105.84	$105.85	$105.80
7 purchase totals =	$943.38		$1,030.5580	$1,030.55	$1,030.55	$1,030.60