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	$66.77	5.515%	$70.4524	$70.45	$70.45	$70.50
Purchase #2	$175.72	7.575%	$189.0308	$189.03	$189.05	$189.00
Purchase #3	$67.34	7.719%	$72.538	$72.54	$72.55	$72.50
Purchase #4	$79.55	10.472%	$87.8805	$87.88	$87.90	$87.90
Purchase #5	$49.82	5.850%	$52.7345	$52.73	$52.75	$52.70
Purchase #6	$189.83	10.645%	$210.0374	$210.04	$210.05	$210.00
Purchase #7	$136.25	5.417%	$143.6307	$143.63	$143.65	$143.60
7 purchase totals =	$765.28		$826.3043	$826.30	$826.40	$826.20