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	$9.89	4.202%	$10.3056	$10.31	$10.30	$10.30
Purchase #2	$59.48	11.526%	$66.3357	$66.34	$66.35	$66.30
Purchase #3	$120.63	9.174%	$131.6966	$131.70	$131.70	$131.70
Purchase #4	$143.59	11.812%	$160.5509	$160.55	$160.55	$160.60
Purchase #5	$79.39	4.173%	$82.7029	$82.70	$82.70	$82.70
Purchase #6	$122.82	4.231%	$128.0165	$128.02	$128.00	$128.00
Purchase #7	$152.83	4.317%	$159.4277	$159.43	$159.45	$159.40
7 purchase totals =	$688.63		$739.0359	$739.05	$739.05	$739.00