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	$105.51	3.506%	$109.2092	$109.21	$109.20	$109.20
Purchase #2	$34.89	12.598%	$39.2854	$39.29	$39.30	$39.30
Purchase #3	$250.29	11.533%	$279.1559	$279.16	$279.15	$279.20
Purchase #4	$31.57	6.282%	$33.5532	$33.55	$33.55	$33.60
Purchase #5	$93.85	6.868%	$100.2956	$100.30	$100.30	$100.30
Purchase #6	$121.47	10.713%	$134.4831	$134.48	$134.50	$134.50
Purchase #7	$147.48	4.556%	$154.1992	$154.20	$154.20	$154.20
7 purchase totals =	$785.06		$850.1816	$850.19	$850.20	$850.30