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	$136.53	6.591%	$145.5287	$145.53	$145.55	$145.50
Purchase #2	$250.51	6.104%	$265.8011	$265.80	$265.80	$265.80
Purchase #3	$54.31	9.612%	$59.5303	$59.53	$59.55	$59.50
Purchase #4	$161.38	13.183%	$182.6547	$182.65	$182.65	$182.70
Purchase #5	$222.45	11.597%	$248.2475	$248.25	$248.25	$248.20
Purchase #6	$65.70	3.277%	$67.853	$67.85	$67.85	$67.90
Purchase #7	$209.66	3.532%	$217.0652	$217.07	$217.05	$217.10
7 purchase totals =	$1,100.54		$1,186.6805	$1,186.68	$1,186.70	$1,186.70