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	$239.42	13.404%	$271.5119	$271.51	$271.50	$271.50
Purchase #2	$35.43	8.240%	$38.3494	$38.35	$38.35	$38.30
Purchase #3	$225.87	6.388%	$240.2986	$240.30	$240.30	$240.30
Purchase #4	$190.90	4.488%	$199.4676	$199.47	$199.45	$199.50
Purchase #5	$213.92	4.549%	$223.6512	$223.65	$223.65	$223.70
Purchase #6	$120.82	12.867%	$136.3659	$136.37	$136.35	$136.40
Purchase #7	$220.95	3.793%	$229.3306	$229.33	$229.35	$229.30
7 purchase totals =	$1,247.31		$1,338.9752	$1,338.98	$1,338.95	$1,339.00