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	$75.68	12.804%	$85.3701	$85.37	$85.35	$85.40
Purchase #2	$60.80	11.143%	$67.5749	$67.57	$67.55	$67.60
Purchase #3	$213.69	13.193%	$241.8821	$241.88	$241.90	$241.90
Purchase #4	$165.75	7.240%	$177.7503	$177.75	$177.75	$177.80
Purchase #5	$174.94	6.844%	$186.9129	$186.91	$186.90	$186.90
Purchase #6	$79.73	4.601%	$83.3984	$83.40	$83.40	$83.40
Purchase #7	$68.37	6.155%	$72.5782	$72.58	$72.60	$72.60
7 purchase totals =	$838.96		$915.4669	$915.46	$915.45	$915.60