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	$85.86	6.672%	$91.5886	$91.59	$91.60	$91.60
Purchase #2	$52.75	11.847%	$58.9993	$59.00	$59.00	$59.00
Purchase #3	$87.90	5.247%	$92.5121	$92.51	$92.50	$92.50
Purchase #4	$113.71	6.201%	$120.7612	$120.76	$120.75	$120.80
Purchase #5	$104.47	11.633%	$116.623	$116.62	$116.60	$116.60
Purchase #6	$173.32	13.511%	$196.7373	$196.74	$196.75	$196.70
Purchase #7	$201.44	7.563%	$216.6749	$216.67	$216.65	$216.70
7 purchase totals =	$819.45		$893.8964	$893.89	$893.85	$893.90