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	$220.80	11.614%	$246.4437	$246.44	$246.45	$246.40
Purchase #2	$137.64	7.104%	$147.4179	$147.42	$147.40	$147.40
Purchase #3	$31.96	12.263%	$35.8793	$35.88	$35.90	$35.90
Purchase #4	$40.78	4.873%	$42.7672	$42.77	$42.75	$42.80
Purchase #5	$90.39	10.735%	$100.0934	$100.09	$100.10	$100.10
Purchase #6	$131.84	9.364%	$144.1855	$144.19	$144.20	$144.20
Purchase #7	$106.86	11.198%	$118.8262	$118.83	$118.85	$118.80
7 purchase totals =	$760.27		$835.6132	$835.62	$835.65	$835.60