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	$39.26	5.763%	$41.5226	$41.52	$41.50	$41.50
Purchase #2	$172.54	10.809%	$191.1898	$191.19	$191.20	$191.20
Purchase #3	$150.63	11.840%	$168.4646	$168.46	$168.45	$168.50
Purchase #4	$235.65	9.786%	$258.7107	$258.71	$258.70	$258.70
Purchase #5	$31.61	9.841%	$34.7207	$34.72	$34.70	$34.70
Purchase #6	$73.54	9.516%	$80.5381	$80.54	$80.55	$80.50
Purchase #7	$30.65	8.404%	$33.2258	$33.23	$33.25	$33.20
7 purchase totals =	$733.88		$808.3723	$808.37	$808.35	$808.30