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	$68.52	6.375%	$72.8882	$72.89	$72.90	$72.90
Purchase #2	$208.85	9.522%	$228.7367	$228.74	$228.75	$228.70
Purchase #3	$163.52	12.780%	$184.4179	$184.42	$184.40	$184.40
Purchase #4	$208.95	6.718%	$222.9873	$222.99	$223.00	$223.00
Purchase #5	$95.79	3.166%	$98.8227	$98.82	$98.80	$98.80
Purchase #6	$73.86	5.710%	$78.0774	$78.08	$78.10	$78.10
Purchase #7	$82.62	10.710%	$91.4686	$91.47	$91.45	$91.50
7 purchase totals =	$902.11		$977.3988	$977.41	$977.40	$977.40