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	$165.95	11.177%	$184.4982	$184.50	$184.50	$184.50
Purchase #2	$111.66	6.728%	$119.1725	$119.17	$119.15	$119.20
Purchase #3	$52.69	10.560%	$58.2541	$58.25	$58.25	$58.30
Purchase #4	$124.25	12.402%	$139.6595	$139.66	$139.65	$139.70
Purchase #5	$247.27	6.825%	$264.1462	$264.15	$264.15	$264.10
Purchase #6	$182.47	7.719%	$196.5549	$196.55	$196.55	$196.60
Purchase #7	$124.35	4.544%	$130.0005	$130.00	$130.00	$130.00
7 purchase totals =	$1,008.64		$1,092.2859	$1,092.28	$1,092.25	$1,092.40