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	$103.27	13.158%	$116.8583	$116.86	$116.85	$116.90
Purchase #2	$212.90	4.347%	$222.1548	$222.15	$222.15	$222.20
Purchase #3	$162.41	9.418%	$177.7058	$177.71	$177.70	$177.70
Purchase #4	$209.41	9.696%	$229.7144	$229.71	$229.70	$229.70
Purchase #5	$144.98	5.786%	$153.3685	$153.37	$153.35	$153.40
Purchase #6	$166.51	3.260%	$171.9382	$171.94	$171.95	$171.90
Purchase #7	$219.46	4.264%	$228.8178	$228.82	$228.80	$228.80
7 purchase totals =	$1,218.94		$1,300.5578	$1,300.56	$1,300.50	$1,300.60