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	$64.96	13.754%	$73.8946	$73.89	$73.90	$73.90
Purchase #2	$65.99	9.199%	$72.0604	$72.06	$72.05	$72.10
Purchase #3	$101.82	6.457%	$108.3945	$108.39	$108.40	$108.40
Purchase #4	$139.90	12.459%	$157.3301	$157.33	$157.35	$157.30
Purchase #5	$45.98	13.634%	$52.2489	$52.25	$52.25	$52.20
Purchase #6	$27.56	4.391%	$28.7702	$28.77	$28.75	$28.80
Purchase #7	$155.89	13.430%	$176.826	$176.83	$176.85	$176.80
7 purchase totals =	$602.10		$669.5247	$669.52	$669.55	$669.50