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	$56.33	6.144%	$59.7909	$59.79	$59.80	$59.80
Purchase #2	$123.82	6.173%	$131.4634	$131.46	$131.45	$131.50
Purchase #3	$113.98	5.154%	$119.8545	$119.85	$119.85	$119.90
Purchase #4	$217.66	13.838%	$247.7798	$247.78	$247.80	$247.80
Purchase #5	$7.76	6.793%	$8.2871	$8.29	$8.30	$8.30
Purchase #6	$181.53	10.469%	$200.5344	$200.53	$200.55	$200.50
Purchase #7	$174.34	3.110%	$179.762	$179.76	$179.75	$179.80
7 purchase totals =	$875.42		$947.4721	$947.46	$947.50	$947.60