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	$63.89	6.469%	$68.023	$68.02	$68.00	$68.00
Purchase #2	$132.37	10.699%	$146.5323	$146.53	$146.55	$146.50
Purchase #3	$19.67	7.749%	$21.1942	$21.19	$21.20	$21.20
Purchase #4	$147.61	6.309%	$156.9227	$156.92	$156.90	$156.90
Purchase #5	$76.86	10.722%	$85.1009	$85.10	$85.10	$85.10
Purchase #6	$98.89	10.734%	$109.5049	$109.50	$109.50	$109.50
Purchase #7	$216.60	12.535%	$243.7508	$243.75	$243.75	$243.80
7 purchase totals =	$755.89		$831.0288	$831.01	$831.00	$831.00