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	$146.72	10.574%	$162.2342	$162.23	$162.25	$162.20
Purchase #2	$67.64	7.598%	$72.7793	$72.78	$72.80	$72.80
Purchase #3	$37.56	3.158%	$38.7461	$38.75	$38.75	$38.70
Purchase #4	$67.48	10.315%	$74.4406	$74.44	$74.45	$74.40
Purchase #5	$19.59	9.735%	$21.4971	$21.50	$21.50	$21.50
Purchase #6	$156.95	7.837%	$169.2502	$169.25	$169.25	$169.30
Purchase #7	$123.95	5.418%	$130.6656	$130.67	$130.65	$130.70
7 purchase totals =	$619.89		$669.6131	$669.62	$669.65	$669.60