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	$52.81	9.625%	$57.893	$57.89	$57.90	$57.90
Purchase #2	$81.39	10.471%	$89.9123	$89.91	$89.90	$89.90
Purchase #3	$217.49	12.551%	$244.7872	$244.79	$244.80	$244.80
Purchase #4	$250.31	9.255%	$273.4762	$273.48	$273.50	$273.50
Purchase #5	$26.34	9.571%	$28.861	$28.86	$28.85	$28.90
Purchase #6	$57.95	10.856%	$64.2411	$64.24	$64.25	$64.20
Purchase #7	$155.44	4.616%	$162.6151	$162.62	$162.60	$162.60
7 purchase totals =	$841.73		$921.7859	$921.79	$921.80	$921.80