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	$249.90	7.329%	$268.2152	$268.22	$268.20	$268.20
Purchase #2	$89.91	6.320%	$95.5923	$95.59	$95.60	$95.60
Purchase #3	$133.66	5.747%	$141.3414	$141.34	$141.35	$141.30
Purchase #4	$128.56	7.501%	$138.2033	$138.20	$138.20	$138.20
Purchase #5	$215.34	11.734%	$240.608	$240.61	$240.60	$240.60
Purchase #6	$60.38	13.431%	$68.4896	$68.49	$68.50	$68.50
Purchase #7	$109.26	13.387%	$123.8866	$123.89	$123.90	$123.90
7 purchase totals =	$987.01		$1,076.3364	$1,076.34	$1,076.35	$1,076.30