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	$7.65	8.425%	$8.2945	$8.29	$8.30	$8.30
Purchase #2	$141.32	10.720%	$156.4695	$156.47	$156.45	$156.50
Purchase #3	$78.99	8.741%	$85.8945	$85.89	$85.90	$85.90
Purchase #4	$232.48	7.710%	$250.4042	$250.40	$250.40	$250.40
Purchase #5	$101.73	10.310%	$112.2184	$112.22	$112.20	$112.20
Purchase #6	$77.96	5.862%	$82.53	$82.53	$82.55	$82.50
Purchase #7	$191.30	4.368%	$199.656	$199.66	$199.65	$199.70
7 purchase totals =	$831.43		$895.4671	$895.46	$895.45	$895.50