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	$93.71	11.610%	$104.5897	$104.59	$104.60	$104.60
Purchase #2	$148.30	13.540%	$168.3798	$168.38	$168.40	$168.40
Purchase #3	$89.71	10.328%	$98.9752	$98.98	$99.00	$99.00
Purchase #4	$139.50	8.239%	$150.9934	$150.99	$151.00	$151.00
Purchase #5	$40.61	6.776%	$43.3617	$43.36	$43.35	$43.40
Purchase #6	$197.58	9.487%	$216.3244	$216.32	$216.30	$216.30
Purchase #7	$215.70	6.523%	$229.7701	$229.77	$229.75	$229.80
7 purchase totals =	$925.11		$1,012.3943	$1,012.39	$1,012.40	$1,012.50