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	$113.36	5.317%	$119.3874	$119.39	$119.40	$119.40
Purchase #2	$85.51	5.192%	$89.9497	$89.95	$89.95	$89.90
Purchase #3	$75.44	4.523%	$78.8522	$78.85	$78.85	$78.90
Purchase #4	$174.28	9.234%	$190.373	$190.37	$190.35	$190.40
Purchase #5	$11.71	7.365%	$12.5724	$12.57	$12.55	$12.60
Purchase #6	$217.85	12.495%	$245.0704	$245.07	$245.05	$245.10
Purchase #7	$79.48	6.468%	$84.6208	$84.62	$84.60	$84.60
7 purchase totals =	$757.63		$820.8259	$820.82	$820.75	$820.90