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	$45.88	9.477%	$50.228	$50.23	$50.25	$50.20
Purchase #2	$49.67	9.418%	$54.3479	$54.35	$54.35	$54.30
Purchase #3	$99.67	7.282%	$106.928	$106.93	$106.95	$106.90
Purchase #4	$231.75	12.824%	$261.4696	$261.47	$261.45	$261.50
Purchase #5	$63.62	9.873%	$69.9012	$69.90	$69.90	$69.90
Purchase #6	$82.39	4.426%	$86.0366	$86.04	$86.05	$86.00
Purchase #7	$36.89	5.639%	$38.9702	$38.97	$38.95	$39.00
7 purchase totals =	$609.87		$667.8815	$667.89	$667.90	$667.80