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	$147.94	5.768%	$156.4732	$156.47	$156.45	$156.50
Purchase #2	$145.80	6.234%	$154.8892	$154.89	$154.90	$154.90
Purchase #3	$137.95	3.151%	$142.2968	$142.30	$142.30	$142.30
Purchase #4	$142.38	12.321%	$159.9226	$159.92	$159.90	$159.90
Purchase #5	$16.51	13.141%	$18.6796	$18.68	$18.70	$18.70
Purchase #6	$58.41	5.306%	$61.5092	$61.51	$61.50	$61.50
Purchase #7	$200.43	11.703%	$223.8863	$223.89	$223.90	$223.90
7 purchase totals =	$849.42		$917.6569	$917.66	$917.65	$917.70