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	$188.86	6.357%	$200.8658	$200.87	$200.85	$200.90
Purchase #2	$85.51	4.710%	$89.5375	$89.54	$89.55	$89.50
Purchase #3	$180.30	9.839%	$198.0397	$198.04	$198.05	$198.00
Purchase #4	$7.81	6.820%	$8.3426	$8.34	$8.35	$8.30
Purchase #5	$173.78	13.731%	$197.6417	$197.64	$197.65	$197.60
Purchase #6	$102.87	8.202%	$111.3074	$111.31	$111.30	$111.30
Purchase #7	$5.67	8.361%	$6.1441	$6.14	$6.15	$6.10
7 purchase totals =	$744.80		$811.8788	$811.88	$811.90	$811.70