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	$181.31	10.766%	$200.8298	$200.83	$200.85	$200.80
Purchase #2	$134.54	8.718%	$146.2692	$146.27	$146.25	$146.30
Purchase #3	$229.80	8.134%	$248.4919	$248.49	$248.50	$248.50
Purchase #4	$206.69	7.596%	$222.3902	$222.39	$222.40	$222.40
Purchase #5	$106.26	6.802%	$113.4878	$113.49	$113.50	$113.50
Purchase #6	$187.51	11.151%	$208.4192	$208.42	$208.40	$208.40
Purchase #7	$75.40	4.610%	$78.8759	$78.88	$78.90	$78.90
7 purchase totals =	$1,121.51		$1,218.7640	$1,218.77	$1,218.80	$1,218.80