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	$221.32	8.842%	$240.8891	$240.89	$240.90	$240.90
Purchase #2	$49.96	12.290%	$56.1001	$56.10	$56.10	$56.10
Purchase #3	$69.98	5.153%	$73.5861	$73.59	$73.60	$73.60
Purchase #4	$47.26	10.661%	$52.2984	$52.30	$52.30	$52.30
Purchase #5	$215.88	12.358%	$242.5585	$242.56	$242.55	$242.60
Purchase #6	$37.59	7.129%	$40.2698	$40.27	$40.25	$40.30
Purchase #7	$243.67	8.628%	$264.6938	$264.69	$264.70	$264.70
7 purchase totals =	$885.66		$970.3958	$970.40	$970.40	$970.50