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	$83.50	5.694%	$88.2545	$88.25	$88.25	$88.30
Purchase #2	$184.25	6.696%	$196.5874	$196.59	$196.60	$196.60
Purchase #3	$73.58	10.799%	$81.5259	$81.53	$81.55	$81.50
Purchase #4	$202.32	8.519%	$219.5556	$219.56	$219.55	$219.60
Purchase #5	$220.34	9.641%	$241.583	$241.58	$241.60	$241.60
Purchase #6	$246.83	11.151%	$274.354	$274.35	$274.35	$274.40
Purchase #7	$80.28	6.651%	$85.6194	$85.62	$85.60	$85.60
7 purchase totals =	$1,091.10		$1,187.4798	$1,187.48	$1,187.50	$1,187.60