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	$231.87	12.388%	$260.5941	$260.59	$260.60	$260.60
Purchase #2	$5.81	3.475%	$6.0119	$6.01	$6.00	$6.00
Purchase #3	$134.52	10.257%	$148.3177	$148.32	$148.30	$148.30
Purchase #4	$239.86	10.435%	$264.8894	$264.89	$264.90	$264.90
Purchase #5	$38.61	10.729%	$42.7525	$42.75	$42.75	$42.80
Purchase #6	$134.50	11.682%	$150.2123	$150.21	$150.20	$150.20
Purchase #7	$137.83	7.491%	$148.1548	$148.15	$148.15	$148.20
7 purchase totals =	$923.00		$1,020.9327	$1,020.92	$1,020.90	$1,021.00