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	$5.37	9.758%	$5.894	$5.89	$5.90	$5.90
Purchase #2	$220.35	9.590%	$241.4816	$241.48	$241.50	$241.50
Purchase #3	$165.33	11.224%	$183.8866	$183.89	$183.90	$183.90
Purchase #4	$88.44	13.315%	$100.2158	$100.22	$100.20	$100.20
Purchase #5	$201.52	7.406%	$216.4446	$216.44	$216.45	$216.40
Purchase #6	$213.56	4.264%	$222.6662	$222.67	$222.65	$222.70
Purchase #7	$72.86	4.515%	$76.1496	$76.15	$76.15	$76.10
7 purchase totals =	$967.43		$1,046.7384	$1,046.74	$1,046.75	$1,046.70