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	$164.46	6.269%	$174.77	$174.77	$174.75	$174.80
Purchase #2	$63.64	10.568%	$70.3655	$70.37	$70.35	$70.40
Purchase #3	$143.48	3.655%	$148.7242	$148.72	$148.70	$148.70
Purchase #4	$54.84	4.756%	$57.4482	$57.45	$57.45	$57.40
Purchase #5	$247.35	10.568%	$273.4899	$273.49	$273.50	$273.50
Purchase #6	$125.26	11.299%	$139.4131	$139.41	$139.40	$139.40
Purchase #7	$154.57	13.407%	$175.2932	$175.29	$175.30	$175.30
7 purchase totals =	$953.60		$1,039.5041	$1,039.50	$1,039.45	$1,039.50