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	$52.81	3.348%	$54.5781	$54.58	$54.60	$54.60
Purchase #2	$19.56	4.700%	$20.4793	$20.48	$20.50	$20.50
Purchase #3	$126.37	8.735%	$137.4084	$137.41	$137.40	$137.40
Purchase #4	$184.80	11.541%	$206.1278	$206.13	$206.15	$206.10
Purchase #5	$194.53	12.221%	$218.3035	$218.30	$218.30	$218.30
Purchase #6	$28.34	11.844%	$31.6966	$31.70	$31.70	$31.70
Purchase #7	$147.47	12.156%	$165.3965	$165.40	$165.40	$165.40
7 purchase totals =	$753.88		$833.9902	$834.00	$834.05	$834.00