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	$74.49	10.618%	$82.3993	$82.40	$82.40	$82.40
Purchase #2	$77.43	11.366%	$86.2307	$86.23	$86.25	$86.20
Purchase #3	$114.48	4.753%	$119.9212	$119.92	$119.90	$119.90
Purchase #4	$36.57	8.197%	$39.5676	$39.57	$39.55	$39.60
Purchase #5	$29.38	5.695%	$31.0532	$31.05	$31.05	$31.10
Purchase #6	$71.53	9.245%	$78.1429	$78.14	$78.15	$78.10
Purchase #7	$196.80	13.622%	$223.6081	$223.61	$223.60	$223.60
7 purchase totals =	$600.68		$660.9230	$660.92	$660.90	$660.90