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	$36.69	9.256%	$40.086	$40.09	$40.10	$40.10
Purchase #2	$176.33	10.187%	$194.2927	$194.29	$194.30	$194.30
Purchase #3	$175.86	11.805%	$196.6203	$196.62	$196.60	$196.60
Purchase #4	$32.89	4.636%	$34.4148	$34.41	$34.40	$34.40
Purchase #5	$130.79	4.718%	$136.9607	$136.96	$136.95	$137.00
Purchase #6	$66.59	9.447%	$72.8808	$72.88	$72.90	$72.90
Purchase #7	$128.80	8.718%	$140.0288	$140.03	$140.05	$140.00
7 purchase totals =	$747.95		$815.2841	$815.28	$815.30	$815.30