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	$45.37	3.347%	$46.8885	$46.89	$46.90	$46.90
Purchase #2	$249.33	11.458%	$277.8982	$277.90	$277.90	$277.90
Purchase #3	$37.60	11.823%	$42.0454	$42.05	$42.05	$42.00
Purchase #4	$137.61	7.353%	$147.7285	$147.73	$147.75	$147.70
Purchase #5	$170.52	7.853%	$183.9109	$183.91	$183.90	$183.90
Purchase #6	$20.51	11.635%	$22.8963	$22.90	$22.90	$22.90
Purchase #7	$220.56	13.393%	$250.0996	$250.10	$250.10	$250.10
7 purchase totals =	$881.50		$971.4674	$971.48	$971.50	$971.40