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	$174.81	7.531%	$187.9749	$187.97	$187.95	$188.00
Purchase #2	$141.67	9.558%	$155.2108	$155.21	$155.20	$155.20
Purchase #3	$57.82	13.181%	$65.4413	$65.44	$65.45	$65.40
Purchase #4	$82.81	9.315%	$90.5238	$90.52	$90.50	$90.50
Purchase #5	$250.86	3.598%	$259.8859	$259.89	$259.90	$259.90
Purchase #6	$183.71	4.746%	$192.4289	$192.43	$192.45	$192.40
Purchase #7	$207.61	9.534%	$227.4035	$227.40	$227.40	$227.40
7 purchase totals =	$1,099.29		$1,178.8691	$1,178.86	$1,178.85	$1,178.80