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	$159.44	3.117%	$164.4097	$164.41	$164.40	$164.40
Purchase #2	$171.37	13.248%	$194.0731	$194.07	$194.05	$194.10
Purchase #3	$184.65	11.315%	$205.5431	$205.54	$205.55	$205.50
Purchase #4	$6.96	5.379%	$7.3344	$7.33	$7.35	$7.30
Purchase #5	$59.90	12.647%	$67.4756	$67.48	$67.50	$67.50
Purchase #6	$102.95	10.349%	$113.6043	$113.60	$113.60	$113.60
Purchase #7	$37.33	7.826%	$40.2514	$40.25	$40.25	$40.30
7 purchase totals =	$722.60		$792.6916	$792.68	$792.70	$792.70