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	$173.29	13.385%	$196.4849	$196.48	$196.50	$196.50
Purchase #2	$24.42	10.442%	$26.9699	$26.97	$26.95	$27.00
Purchase #3	$92.34	8.306%	$100.0098	$100.01	$100.00	$100.00
Purchase #4	$210.66	13.191%	$238.4482	$238.45	$238.45	$238.40
Purchase #5	$202.51	8.549%	$219.8226	$219.82	$219.80	$219.80
Purchase #6	$193.52	13.183%	$219.0317	$219.03	$219.05	$219.00
Purchase #7	$84.54	6.705%	$90.2084	$90.21	$90.20	$90.20
7 purchase totals =	$981.28		$1,090.9755	$1,090.97	$1,090.95	$1,090.90