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	$147.44	8.110%	$159.3974	$159.40	$159.40	$159.40
Purchase #2	$187.51	3.102%	$193.3266	$193.33	$193.35	$193.30
Purchase #3	$215.44	3.746%	$223.5104	$223.51	$223.50	$223.50
Purchase #4	$171.86	9.319%	$187.8756	$187.88	$187.90	$187.90
Purchase #5	$40.83	6.749%	$43.5856	$43.59	$43.60	$43.60
Purchase #6	$59.43	6.817%	$63.4813	$63.48	$63.50	$63.50
Purchase #7	$66.82	4.258%	$69.6652	$69.67	$69.65	$69.70
7 purchase totals =	$889.33		$940.8421	$940.86	$940.90	$940.90