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	$54.34	11.833%	$60.7701	$60.77	$60.75	$60.80
Purchase #2	$180.28	5.856%	$190.8372	$190.84	$190.85	$190.80
Purchase #3	$35.59	10.826%	$39.443	$39.44	$39.45	$39.40
Purchase #4	$6.70	13.548%	$7.6077	$7.61	$7.60	$7.60
Purchase #5	$249.84	12.626%	$281.3848	$281.38	$281.40	$281.40
Purchase #6	$82.85	3.235%	$85.5302	$85.53	$85.55	$85.50
Purchase #7	$119.44	11.811%	$133.5471	$133.55	$133.55	$133.50
7 purchase totals =	$729.04		$799.1201	$799.12	$799.15	$799.00