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	$7.42	12.356%	$8.3368	$8.34	$8.35	$8.30
Purchase #2	$62.89	12.270%	$70.6066	$70.61	$70.60	$70.60
Purchase #3	$37.66	7.569%	$40.5105	$40.51	$40.50	$40.50
Purchase #4	$63.31	6.747%	$67.5815	$67.58	$67.60	$67.60
Purchase #5	$239.34	7.152%	$256.4576	$256.46	$256.45	$256.50
Purchase #6	$94.32	4.470%	$98.5361	$98.54	$98.55	$98.50
Purchase #7	$213.85	12.549%	$240.686	$240.69	$240.70	$240.70
7 purchase totals =	$718.79		$782.7151	$782.73	$782.75	$782.70