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	$5.54	6.415%	$5.8954	$5.90	$5.90	$5.90
Purchase #2	$243.59	12.863%	$274.923	$274.92	$274.90	$274.90
Purchase #3	$177.31	3.709%	$183.8864	$183.89	$183.90	$183.90
Purchase #4	$102.25	6.513%	$108.9095	$108.91	$108.90	$108.90
Purchase #5	$99.32	5.867%	$105.1471	$105.15	$105.15	$105.10
Purchase #6	$73.60	8.151%	$79.5991	$79.60	$79.60	$79.60
Purchase #7	$65.48	12.230%	$73.4882	$73.49	$73.50	$73.50
7 purchase totals =	$767.09		$831.8487	$831.86	$831.85	$831.80