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	$83.94	5.782%	$88.7934	$88.79	$88.80	$88.80
Purchase #2	$17.48	12.191%	$19.611	$19.61	$19.60	$19.60
Purchase #3	$140.57	11.606%	$156.8846	$156.88	$156.90	$156.90
Purchase #4	$106.48	11.107%	$118.3067	$118.31	$118.30	$118.30
Purchase #5	$53.97	7.124%	$57.8148	$57.81	$57.80	$57.80
Purchase #6	$109.25	12.872%	$123.3127	$123.31	$123.30	$123.30
Purchase #7	$228.88	11.636%	$255.5125	$255.51	$255.50	$255.50
7 purchase totals =	$740.57		$820.2357	$820.22	$820.20	$820.20