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	$31.28	12.806%	$35.2857	$35.29	$35.30	$35.30
Purchase #2	$149.59	7.313%	$160.5295	$160.53	$160.55	$160.50
Purchase #3	$95.32	9.655%	$104.5231	$104.52	$104.50	$104.50
Purchase #4	$19.84	10.334%	$21.8903	$21.89	$21.90	$21.90
Purchase #5	$136.50	8.363%	$147.9155	$147.92	$147.90	$147.90
Purchase #6	$129.25	11.348%	$143.9173	$143.92	$143.90	$143.90
Purchase #7	$229.87	10.244%	$253.4179	$253.42	$253.40	$253.40
7 purchase totals =	$791.65		$867.4793	$867.49	$867.45	$867.40