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	$248.47	7.866%	$268.0147	$268.01	$268.00	$268.00
Purchase #2	$82.59	8.755%	$89.8208	$89.82	$89.80	$89.80
Purchase #3	$134.45	4.807%	$140.913	$140.91	$140.90	$140.90
Purchase #4	$170.83	7.321%	$183.3365	$183.34	$183.35	$183.30
Purchase #5	$90.42	11.471%	$100.7921	$100.79	$100.80	$100.80
Purchase #6	$5.25	7.444%	$5.6408	$5.64	$5.65	$5.60
Purchase #7	$26.86	6.103%	$28.4993	$28.50	$28.50	$28.50
7 purchase totals =	$758.87		$817.0172	$817.01	$817.00	$816.90