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	$78.61	12.635%	$88.5424	$88.54	$88.55	$88.50
Purchase #2	$117.58	10.318%	$129.7119	$129.71	$129.70	$129.70
Purchase #3	$158.61	6.585%	$169.0545	$169.05	$169.05	$169.10
Purchase #4	$120.78	10.328%	$133.2542	$133.25	$133.25	$133.30
Purchase #5	$224.98	13.393%	$255.1116	$255.11	$255.10	$255.10
Purchase #6	$90.81	6.307%	$96.5374	$96.54	$96.55	$96.50
Purchase #7	$247.42	3.756%	$256.7131	$256.71	$256.70	$256.70
7 purchase totals =	$1,038.79		$1,128.9251	$1,128.91	$1,128.90	$1,128.90