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	$126.51	3.708%	$131.201	$131.20	$131.20	$131.20
Purchase #2	$74.47	10.839%	$82.5418	$82.54	$82.55	$82.50
Purchase #3	$122.46	11.795%	$136.9042	$136.90	$136.90	$136.90
Purchase #4	$31.38	7.468%	$33.7235	$33.72	$33.70	$33.70
Purchase #5	$206.79	7.802%	$222.9238	$222.92	$222.90	$222.90
Purchase #6	$133.25	5.554%	$140.6507	$140.65	$140.65	$140.70
Purchase #7	$148.89	8.537%	$161.6007	$161.60	$161.60	$161.60
7 purchase totals =	$843.75		$909.5457	$909.53	$909.50	$909.50