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	$54.94	5.171%	$57.7809	$57.78	$57.80	$57.80
Purchase #2	$37.74	7.534%	$40.5833	$40.58	$40.60	$40.60
Purchase #3	$90.39	10.167%	$99.58	$99.58	$99.60	$99.60
Purchase #4	$159.73	7.322%	$171.4254	$171.43	$171.45	$171.40
Purchase #5	$6.85	6.750%	$7.3124	$7.31	$7.30	$7.30
Purchase #6	$189.79	3.646%	$196.7097	$196.71	$196.70	$196.70
Purchase #7	$156.34	13.461%	$177.3849	$177.38	$177.40	$177.40
7 purchase totals =	$695.78		$750.7766	$750.77	$750.85	$750.80