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	$12.39	10.474%	$13.6877	$13.69	$13.70	$13.70
Purchase #2	$246.52	9.501%	$269.9419	$269.94	$269.95	$269.90
Purchase #3	$150.56	3.203%	$155.3824	$155.38	$155.40	$155.40
Purchase #4	$219.44	12.495%	$246.859	$246.86	$246.85	$246.90
Purchase #5	$207.79	10.392%	$229.3835	$229.38	$229.40	$229.40
Purchase #6	$72.33	13.292%	$81.9441	$81.94	$81.95	$81.90
Purchase #7	$140.79	9.124%	$153.6357	$153.64	$153.65	$153.60
7 purchase totals =	$1,049.82		$1,150.8343	$1,150.83	$1,150.90	$1,150.80