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	$194.57	13.336%	$220.5179	$220.52	$220.50	$220.50
Purchase #2	$18.79	10.585%	$20.7789	$20.78	$20.80	$20.80
Purchase #3	$89.83	6.502%	$95.6707	$95.67	$95.65	$95.70
Purchase #4	$198.82	13.139%	$224.943	$224.94	$224.95	$224.90
Purchase #5	$139.82	12.187%	$156.8599	$156.86	$156.85	$156.90
Purchase #6	$147.70	9.377%	$161.5498	$161.55	$161.55	$161.50
Purchase #7	$154.42	3.544%	$159.8926	$159.89	$159.90	$159.90
7 purchase totals =	$943.95		$1,040.2128	$1,040.21	$1,040.20	$1,040.20