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	$232.94	7.282%	$249.9027	$249.90	$249.90	$249.90
Purchase #2	$47.43	10.701%	$52.5055	$52.51	$52.50	$52.50
Purchase #3	$190.58	10.663%	$210.9015	$210.90	$210.90	$210.90
Purchase #4	$158.47	8.726%	$172.2981	$172.30	$172.30	$172.30
Purchase #5	$71.46	8.204%	$77.3226	$77.32	$77.30	$77.30
Purchase #6	$215.90	10.701%	$239.0035	$239.00	$239.00	$239.00
Purchase #7	$86.31	5.341%	$90.9198	$90.92	$90.90	$90.90
7 purchase totals =	$1,003.09		$1,092.8537	$1,092.85	$1,092.80	$1,092.80