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	$46.46	9.856%	$51.0391	$51.04	$51.05	$51.00
Purchase #2	$211.63	10.797%	$234.4797	$234.48	$234.50	$234.50
Purchase #3	$146.99	3.484%	$152.1111	$152.11	$152.10	$152.10
Purchase #4	$69.62	3.239%	$71.875	$71.88	$71.90	$71.90
Purchase #5	$197.36	5.498%	$208.2109	$208.21	$208.20	$208.20
Purchase #6	$37.68	12.659%	$42.4499	$42.45	$42.45	$42.40
Purchase #7	$39.74	6.694%	$42.4002	$42.40	$42.40	$42.40
7 purchase totals =	$749.48		$802.5659	$802.57	$802.60	$802.50