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	$34.68	8.166%	$37.512	$37.51	$37.50	$37.50
Purchase #2	$110.73	11.191%	$123.1218	$123.12	$123.10	$123.10
Purchase #3	$68.81	11.256%	$76.5553	$76.56	$76.55	$76.60
Purchase #4	$168.89	4.718%	$176.8582	$176.86	$176.85	$176.90
Purchase #5	$140.35	6.838%	$149.9471	$149.95	$149.95	$149.90
Purchase #6	$205.80	5.502%	$217.1231	$217.12	$217.10	$217.10
Purchase #7	$182.89	8.166%	$197.8248	$197.82	$197.80	$197.80
7 purchase totals =	$912.15		$978.9423	$978.94	$978.85	$978.90