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	$17.55	3.467%	$18.1585	$18.16	$18.15	$18.20
Purchase #2	$51.84	4.179%	$54.0064	$54.01	$54.00	$54.00
Purchase #3	$73.39	7.404%	$78.8238	$78.82	$78.80	$78.80
Purchase #4	$196.73	6.830%	$210.1667	$210.17	$210.15	$210.20
Purchase #5	$233.50	4.726%	$244.5352	$244.54	$244.55	$244.50
Purchase #6	$103.82	9.609%	$113.7961	$113.80	$113.80	$113.80
Purchase #7	$183.76	12.210%	$206.1971	$206.20	$206.20	$206.20
7 purchase totals =	$860.59		$925.6838	$925.70	$925.65	$925.70