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	$245.72	8.597%	$266.8445	$266.84	$266.85	$266.80
Purchase #2	$88.25	3.770%	$91.577	$91.58	$91.60	$91.60
Purchase #3	$129.80	8.761%	$141.1718	$141.17	$141.15	$141.20
Purchase #4	$168.70	6.229%	$179.2083	$179.21	$179.20	$179.20
Purchase #5	$123.37	6.445%	$131.3212	$131.32	$131.30	$131.30
Purchase #6	$112.74	8.696%	$122.5439	$122.54	$122.55	$122.50
Purchase #7	$41.56	9.812%	$45.6379	$45.64	$45.65	$45.60
7 purchase totals =	$910.14		$978.3046	$978.30	$978.30	$978.20