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	$203.45	9.829%	$223.4471	$223.45	$223.45	$223.40
Purchase #2	$62.81	3.133%	$64.7778	$64.78	$64.80	$64.80
Purchase #3	$120.40	8.479%	$130.6087	$130.61	$130.60	$130.60
Purchase #4	$150.95	12.444%	$169.7342	$169.73	$169.75	$169.70
Purchase #5	$24.73	3.133%	$25.5048	$25.50	$25.50	$25.50
Purchase #6	$29.91	13.480%	$33.9419	$33.94	$33.95	$33.90
Purchase #7	$82.57	8.616%	$89.6842	$89.68	$89.70	$89.70
7 purchase totals =	$674.82		$737.6987	$737.69	$737.75	$737.60