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	$87.88	12.459%	$98.829	$98.83	$98.85	$98.80
Purchase #2	$200.63	12.597%	$225.9034	$225.90	$225.90	$225.90
Purchase #3	$202.67	3.144%	$209.0419	$209.04	$209.05	$209.00
Purchase #4	$196.79	4.271%	$205.1949	$205.19	$205.20	$205.20
Purchase #5	$21.25	5.461%	$22.4105	$22.41	$22.40	$22.40
Purchase #6	$68.92	13.756%	$78.4006	$78.40	$78.40	$78.40
Purchase #7	$87.89	13.807%	$100.025	$100.03	$100.05	$100.00
7 purchase totals =	$866.03		$939.8053	$939.80	$939.85	$939.70