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	$125.90	4.799%	$131.9419	$131.94	$131.95	$131.90
Purchase #2	$146.61	10.540%	$162.0627	$162.06	$162.05	$162.10
Purchase #3	$212.27	8.821%	$230.9943	$230.99	$231.00	$231.00
Purchase #4	$109.43	12.408%	$123.0081	$123.01	$123.00	$123.00
Purchase #5	$6.31	11.862%	$7.0585	$7.06	$7.05	$7.10
Purchase #6	$147.27	13.342%	$166.9188	$166.92	$166.90	$166.90
Purchase #7	$146.58	5.836%	$155.1344	$155.13	$155.15	$155.10
7 purchase totals =	$894.37		$977.1187	$977.11	$977.10	$977.10