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	$29.94	11.264%	$33.3124	$33.31	$33.30	$33.30
Purchase #2	$82.52	7.112%	$88.3888	$88.39	$88.40	$88.40
Purchase #3	$82.42	4.679%	$86.2764	$86.28	$86.30	$86.30
Purchase #4	$249.80	9.188%	$272.7516	$272.75	$272.75	$272.80
Purchase #5	$18.57	6.642%	$19.8034	$19.80	$19.80	$19.80
Purchase #6	$36.34	12.530%	$40.8934	$40.89	$40.90	$40.90
Purchase #7	$19.62	9.556%	$21.4949	$21.49	$21.50	$21.50
7 purchase totals =	$519.21		$562.9209	$562.91	$562.95	$563.00