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	$53.90	3.825%	$55.9617	$55.96	$55.95	$56.00
Purchase #2	$39.50	6.104%	$41.9111	$41.91	$41.90	$41.90
Purchase #3	$85.69	7.800%	$92.3738	$92.37	$92.35	$92.40
Purchase #4	$57.74	11.199%	$64.2063	$64.21	$64.20	$64.20
Purchase #5	$59.29	5.428%	$62.5083	$62.51	$62.50	$62.50
Purchase #6	$113.43	9.149%	$123.8077	$123.81	$123.80	$123.80
Purchase #7	$197.60	13.587%	$224.4479	$224.45	$224.45	$224.40
7 purchase totals =	$607.15		$665.2168	$665.22	$665.15	$665.20