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	$35.89	13.689%	$40.803	$40.80	$40.80	$40.80
Purchase #2	$133.72	7.614%	$143.9014	$143.90	$143.90	$143.90
Purchase #3	$82.56	4.699%	$86.4395	$86.44	$86.45	$86.40
Purchase #4	$81.37	11.717%	$90.9041	$90.90	$90.90	$90.90
Purchase #5	$223.78	12.547%	$251.8577	$251.86	$251.85	$251.90
Purchase #6	$155.71	13.793%	$177.1871	$177.19	$177.20	$177.20
Purchase #7	$78.52	6.479%	$83.6073	$83.61	$83.60	$83.60
7 purchase totals =	$791.55		$874.7001	$874.70	$874.70	$874.70