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	$50.35	12.499%	$56.6432	$56.64	$56.65	$56.60
Purchase #2	$43.45	4.289%	$45.3136	$45.31	$45.30	$45.30
Purchase #3	$80.90	9.663%	$88.7174	$88.72	$88.70	$88.70
Purchase #4	$224.36	9.457%	$245.5777	$245.58	$245.60	$245.60
Purchase #5	$46.71	9.200%	$51.0073	$51.01	$51.00	$51.00
Purchase #6	$200.50	5.628%	$211.7841	$211.78	$211.80	$211.80
Purchase #7	$150.73	11.804%	$168.5222	$168.52	$168.50	$168.50
7 purchase totals =	$797.00		$867.5655	$867.56	$867.55	$867.50