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	$133.90	10.173%	$147.5216	$147.52	$147.50	$147.50
Purchase #2	$166.45	11.433%	$185.4802	$185.48	$185.50	$185.50
Purchase #3	$152.81	10.549%	$168.9299	$168.93	$168.95	$168.90
Purchase #4	$199.86	8.328%	$216.5043	$216.50	$216.50	$216.50
Purchase #5	$170.99	9.683%	$187.547	$187.55	$187.55	$187.50
Purchase #6	$131.48	8.741%	$142.9727	$142.97	$142.95	$143.00
Purchase #7	$219.29	7.555%	$235.8574	$235.86	$235.85	$235.90
7 purchase totals =	$1,174.78		$1,284.8131	$1,284.81	$1,284.80	$1,284.80