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	$58.37	13.256%	$66.1075	$66.11	$66.10	$66.10
Purchase #2	$79.70	12.104%	$89.3469	$89.35	$89.35	$89.30
Purchase #3	$38.72	6.434%	$41.2112	$41.21	$41.20	$41.20
Purchase #4	$86.96	3.785%	$90.2514	$90.25	$90.25	$90.30
Purchase #5	$131.94	11.621%	$147.2727	$147.27	$147.25	$147.30
Purchase #6	$32.80	8.257%	$35.5083	$35.51	$35.50	$35.50
Purchase #7	$93.51	7.828%	$100.83	$100.83	$100.85	$100.80
7 purchase totals =	$522.00		$570.5280	$570.53	$570.50	$570.50