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	$7.52	4.770%	$7.8787	$7.88	$7.90	$7.90
Purchase #2	$218.66	7.429%	$234.9043	$234.90	$234.90	$234.90
Purchase #3	$70.63	5.537%	$74.5408	$74.54	$74.55	$74.50
Purchase #4	$136.97	6.515%	$145.8936	$145.89	$145.90	$145.90
Purchase #5	$95.40	5.739%	$100.875	$100.88	$100.90	$100.90
Purchase #6	$203.34	8.108%	$219.8268	$219.83	$219.85	$219.80
Purchase #7	$150.61	3.279%	$155.5485	$155.55	$155.55	$155.50
7 purchase totals =	$883.13		$939.4677	$939.47	$939.55	$939.40