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	$165.74	6.511%	$176.5313	$176.53	$176.55	$176.50
Purchase #2	$134.60	5.789%	$142.392	$142.39	$142.40	$142.40
Purchase #3	$55.36	11.257%	$61.5919	$61.59	$61.60	$61.60
Purchase #4	$124.56	8.762%	$135.4739	$135.47	$135.45	$135.50
Purchase #5	$30.37	11.737%	$33.9345	$33.93	$33.95	$33.90
Purchase #6	$81.56	11.164%	$90.6654	$90.67	$90.65	$90.70
Purchase #7	$30.61	10.425%	$33.8011	$33.80	$33.80	$33.80
7 purchase totals =	$622.80		$674.3901	$674.38	$674.40	$674.40