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	$215.46	6.420%	$229.2925	$229.29	$229.30	$229.30
Purchase #2	$28.62	11.578%	$31.9336	$31.93	$31.95	$31.90
Purchase #3	$74.95	13.367%	$84.9686	$84.97	$84.95	$85.00
Purchase #4	$29.75	12.529%	$33.4774	$33.48	$33.50	$33.50
Purchase #5	$99.53	9.187%	$108.6738	$108.67	$108.65	$108.70
Purchase #6	$172.72	10.289%	$190.4912	$190.49	$190.50	$190.50
Purchase #7	$148.80	13.503%	$168.8925	$168.89	$168.90	$168.90
7 purchase totals =	$769.83		$847.7296	$847.72	$847.75	$847.80