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	$17.51	5.804%	$18.5263	$18.53	$18.55	$18.50
Purchase #2	$181.44	8.373%	$196.632	$196.63	$196.65	$196.60
Purchase #3	$28.29	12.246%	$31.7544	$31.75	$31.75	$31.80
Purchase #4	$75.78	10.514%	$83.7475	$83.75	$83.75	$83.70
Purchase #5	$139.94	10.700%	$154.9136	$154.91	$154.90	$154.90
Purchase #6	$88.25	4.627%	$92.3333	$92.33	$92.35	$92.30
Purchase #7	$189.90	5.555%	$200.4489	$200.45	$200.45	$200.40
7 purchase totals =	$721.11		$778.3560	$778.35	$778.40	$778.20