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	$237.38	5.689%	$250.8845	$250.88	$250.90	$250.90
Purchase #2	$54.97	13.213%	$62.2332	$62.23	$62.25	$62.20
Purchase #3	$52.67	5.427%	$55.5284	$55.53	$55.55	$55.50
Purchase #4	$98.46	11.247%	$109.5338	$109.53	$109.55	$109.50
Purchase #5	$38.35	6.233%	$40.7404	$40.74	$40.75	$40.70
Purchase #6	$52.98	10.639%	$58.6165	$58.62	$58.60	$58.60
Purchase #7	$210.59	12.340%	$236.5768	$236.58	$236.60	$236.60
7 purchase totals =	$745.40		$814.1136	$814.11	$814.20	$814.00