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	$30.79	6.423%	$32.7676	$32.77	$32.75	$32.80
Purchase #2	$50.52	5.664%	$53.3815	$53.38	$53.40	$53.40
Purchase #3	$113.49	5.720%	$119.9816	$119.98	$120.00	$120.00
Purchase #4	$71.54	9.679%	$78.4644	$78.46	$78.45	$78.50
Purchase #5	$24.41	3.387%	$25.2368	$25.24	$25.25	$25.20
Purchase #6	$185.63	3.854%	$192.7842	$192.78	$192.80	$192.80
Purchase #7	$216.85	12.171%	$243.2428	$243.24	$243.25	$243.20
7 purchase totals =	$693.23		$745.8589	$745.85	$745.90	$745.90