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	$139.98	13.693%	$159.1475	$159.15	$159.15	$159.10
Purchase #2	$152.61	10.716%	$168.9637	$168.96	$168.95	$169.00
Purchase #3	$152.43	4.666%	$159.5424	$159.54	$159.55	$159.50
Purchase #4	$5.86	12.251%	$6.5779	$6.58	$6.60	$6.60
Purchase #5	$151.37	13.447%	$171.7247	$171.72	$171.70	$171.70
Purchase #6	$55.78	5.782%	$59.0052	$59.01	$59.00	$59.00
Purchase #7	$229.54	13.332%	$260.1423	$260.14	$260.15	$260.10
7 purchase totals =	$887.57		$985.1037	$985.10	$985.10	$985.00