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	$127.89	3.576%	$132.4633	$132.46	$132.45	$132.50
Purchase #2	$217.53	10.489%	$240.3467	$240.35	$240.35	$240.30
Purchase #3	$112.85	6.508%	$120.1943	$120.19	$120.20	$120.20
Purchase #4	$26.40	11.783%	$29.5107	$29.51	$29.50	$29.50
Purchase #5	$119.84	11.646%	$133.7966	$133.80	$133.80	$133.80
Purchase #6	$135.75	10.699%	$150.2739	$150.27	$150.25	$150.30
Purchase #7	$56.40	6.139%	$59.8624	$59.86	$59.85	$59.90
7 purchase totals =	$796.66		$866.4479	$866.44	$866.40	$866.50