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	$174.56	9.252%	$190.7103	$190.71	$190.70	$190.70
Purchase #2	$73.95	6.499%	$78.756	$78.76	$78.75	$78.80
Purchase #3	$56.47	7.350%	$60.6205	$60.62	$60.60	$60.60
Purchase #4	$216.30	7.462%	$232.4403	$232.44	$232.45	$232.40
Purchase #5	$73.50	9.181%	$80.248	$80.25	$80.25	$80.20
Purchase #6	$120.95	8.334%	$131.03	$131.03	$131.05	$131.00
Purchase #7	$38.30	10.853%	$42.4567	$42.46	$42.45	$42.50
7 purchase totals =	$754.03		$816.2618	$816.27	$816.25	$816.20