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	$78.56	13.849%	$89.4398	$89.44	$89.45	$89.40
Purchase #2	$70.33	3.384%	$72.71	$72.71	$72.70	$72.70
Purchase #3	$217.88	11.758%	$243.4983	$243.50	$243.50	$243.50
Purchase #4	$115.29	11.521%	$128.5726	$128.57	$128.55	$128.60
Purchase #5	$123.69	8.155%	$133.7769	$133.78	$133.80	$133.80
Purchase #6	$101.29	4.539%	$105.8876	$105.89	$105.90	$105.90
Purchase #7	$196.43	9.487%	$215.0653	$215.07	$215.05	$215.10
7 purchase totals =	$903.47		$988.9505	$988.96	$988.95	$989.00