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	$189.88	13.484%	$215.4834	$215.48	$215.50	$215.50
Purchase #2	$159.72	9.353%	$174.6586	$174.66	$174.65	$174.70
Purchase #3	$25.49	11.557%	$28.4359	$28.44	$28.45	$28.40
Purchase #4	$40.30	8.412%	$43.69	$43.69	$43.70	$43.70
Purchase #5	$188.86	3.761%	$195.963	$195.96	$195.95	$196.00
Purchase #6	$100.98	11.689%	$112.7836	$112.78	$112.80	$112.80
Purchase #7	$220.58	5.110%	$231.8516	$231.85	$231.85	$231.90
7 purchase totals =	$925.81		$1,002.8661	$1,002.86	$1,002.90	$1,003.00