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	$35.87	12.176%	$40.2375	$40.24	$40.25	$40.20
Purchase #2	$210.76	8.282%	$228.2151	$228.22	$228.20	$228.20
Purchase #3	$73.63	6.451%	$78.3799	$78.38	$78.40	$78.40
Purchase #4	$173.90	11.770%	$194.368	$194.37	$194.35	$194.40
Purchase #5	$215.89	10.570%	$238.7096	$238.71	$238.70	$238.70
Purchase #6	$90.94	9.594%	$99.6648	$99.66	$99.65	$99.70
Purchase #7	$187.82	6.675%	$200.357	$200.36	$200.35	$200.40
7 purchase totals =	$988.81		$1,079.9319	$1,079.94	$1,079.90	$1,080.00