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	$74.87	10.139%	$82.4611	$82.46	$82.45	$82.50
Purchase #2	$36.61	10.826%	$40.5734	$40.57	$40.55	$40.60
Purchase #3	$92.91	13.489%	$105.4426	$105.44	$105.45	$105.40
Purchase #4	$81.81	9.263%	$89.3881	$89.39	$89.40	$89.40
Purchase #5	$147.53	12.481%	$165.9432	$165.94	$165.95	$165.90
Purchase #6	$130.35	9.292%	$142.4621	$142.46	$142.45	$142.50
Purchase #7	$154.81	12.150%	$173.6194	$173.62	$173.60	$173.60
7 purchase totals =	$718.89		$799.8899	$799.88	$799.85	$799.90