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	$28.73	10.543%	$31.759	$31.76	$31.75	$31.80
Purchase #2	$225.45	7.490%	$242.3362	$242.34	$242.35	$242.30
Purchase #3	$199.42	12.711%	$224.7683	$224.77	$224.75	$224.80
Purchase #4	$12.76	4.179%	$13.2932	$13.29	$13.30	$13.30
Purchase #5	$86.60	13.455%	$98.252	$98.25	$98.25	$98.30
Purchase #6	$228.98	13.224%	$259.2603	$259.26	$259.25	$259.30
Purchase #7	$155.54	11.108%	$172.8174	$172.82	$172.80	$172.80
7 purchase totals =	$937.48		$1,042.4864	$1,042.49	$1,042.45	$1,042.60