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	$100.26	3.230%	$103.4984	$103.50	$103.50	$103.50
Purchase #2	$215.59	6.609%	$229.8383	$229.84	$229.85	$229.80
Purchase #3	$34.31	11.207%	$38.1551	$38.16	$38.15	$38.20
Purchase #4	$164.94	6.280%	$175.2982	$175.30	$175.30	$175.30
Purchase #5	$70.90	10.315%	$78.2133	$78.21	$78.20	$78.20
Purchase #6	$16.81	8.662%	$18.2661	$18.27	$18.25	$18.30
Purchase #7	$151.66	11.401%	$168.9508	$168.95	$168.95	$169.00
7 purchase totals =	$754.47		$812.2202	$812.23	$812.20	$812.30