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	$240.55	3.854%	$249.8208	$249.82	$249.80	$249.80
Purchase #2	$101.81	3.192%	$105.0598	$105.06	$105.05	$105.10
Purchase #3	$30.33	12.299%	$34.0603	$34.06	$34.05	$34.10
Purchase #4	$145.39	4.185%	$151.4746	$151.47	$151.45	$151.50
Purchase #5	$51.92	8.315%	$56.2371	$56.24	$56.25	$56.20
Purchase #6	$168.61	6.475%	$179.5275	$179.53	$179.55	$179.50
Purchase #7	$206.71	11.225%	$229.9132	$229.91	$229.90	$229.90
7 purchase totals =	$945.32		$1,006.0933	$1,006.09	$1,006.05	$1,006.10