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	$67.58	8.849%	$73.5602	$73.56	$73.55	$73.60
Purchase #2	$183.56	3.829%	$190.5885	$190.59	$190.60	$190.60
Purchase #3	$153.82	11.230%	$171.094	$171.09	$171.10	$171.10
Purchase #4	$201.98	10.106%	$222.3921	$222.39	$222.40	$222.40
Purchase #5	$82.73	3.537%	$85.6562	$85.66	$85.65	$85.70
Purchase #6	$151.99	3.821%	$157.7975	$157.80	$157.80	$157.80
Purchase #7	$82.43	4.732%	$86.3306	$86.33	$86.35	$86.30
7 purchase totals =	$924.09		$987.4191	$987.42	$987.45	$987.50