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	$248.86	9.723%	$273.0567	$273.06	$273.05	$273.10
Purchase #2	$36.57	4.822%	$38.3334	$38.33	$38.35	$38.30
Purchase #3	$223.92	9.575%	$245.3603	$245.36	$245.35	$245.40
Purchase #4	$63.50	5.530%	$67.0116	$67.01	$67.00	$67.00
Purchase #5	$191.78	12.456%	$215.6681	$215.67	$215.65	$215.70
Purchase #6	$113.93	3.416%	$117.8218	$117.82	$117.80	$117.80
Purchase #7	$41.31	11.110%	$45.8995	$45.90	$45.90	$45.90
7 purchase totals =	$919.87		$1,003.1514	$1,003.15	$1,003.10	$1,003.20