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	$187.28	7.179%	$200.7248	$200.72	$200.70	$200.70
Purchase #2	$16.78	9.404%	$18.358	$18.36	$18.35	$18.40
Purchase #3	$113.72	6.639%	$121.2699	$121.27	$121.25	$121.30
Purchase #4	$208.89	7.642%	$224.8534	$224.85	$224.85	$224.90
Purchase #5	$56.88	4.177%	$59.2559	$59.26	$59.25	$59.30
Purchase #6	$238.71	9.164%	$260.5854	$260.59	$260.60	$260.60
Purchase #7	$31.30	8.257%	$33.8844	$33.88	$33.90	$33.90
7 purchase totals =	$853.56		$918.9318	$918.93	$918.90	$919.10