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	$37.44	8.752%	$40.7167	$40.72	$40.70	$40.70
Purchase #2	$245.85	4.377%	$256.6109	$256.61	$256.60	$256.60
Purchase #3	$77.40	3.786%	$80.3304	$80.33	$80.35	$80.30
Purchase #4	$177.98	13.287%	$201.6282	$201.63	$201.65	$201.60
Purchase #5	$152.45	12.419%	$171.3828	$171.38	$171.40	$171.40
Purchase #6	$64.88	9.654%	$71.1435	$71.14	$71.15	$71.10
Purchase #7	$196.75	10.260%	$216.9366	$216.94	$216.95	$216.90
7 purchase totals =	$952.75		$1,038.7491	$1,038.75	$1,038.80	$1,038.60