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	$76.79	11.865%	$85.9011	$85.90	$85.90	$85.90
Purchase #2	$238.31	9.173%	$260.1702	$260.17	$260.15	$260.20
Purchase #3	$10.99	11.233%	$12.2245	$12.22	$12.20	$12.20
Purchase #4	$186.94	5.202%	$196.6646	$196.66	$196.65	$196.70
Purchase #5	$135.76	12.516%	$152.7517	$152.75	$152.75	$152.80
Purchase #6	$27.30	11.785%	$30.5173	$30.52	$30.50	$30.50
Purchase #7	$41.80	9.223%	$45.6552	$45.66	$45.65	$45.70
7 purchase totals =	$717.89		$783.8846	$783.88	$783.80	$784.00