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	$76.52	9.629%	$83.8881	$83.89	$83.90	$83.90
Purchase #2	$105.81	7.750%	$114.0103	$114.01	$114.00	$114.00
Purchase #3	$247.91	9.673%	$271.8903	$271.89	$271.90	$271.90
Purchase #4	$84.48	7.454%	$90.7771	$90.78	$90.80	$90.80
Purchase #5	$238.95	4.168%	$248.9094	$248.91	$248.90	$248.90
Purchase #6	$225.49	10.780%	$249.7978	$249.80	$249.80	$249.80
Purchase #7	$86.83	5.271%	$91.4068	$91.41	$91.40	$91.40
7 purchase totals =	$1,065.99		$1,150.6798	$1,150.69	$1,150.70	$1,150.70