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	$33.80	8.289%	$36.6017	$36.60	$36.60	$36.60
Purchase #2	$175.53	5.157%	$184.5821	$184.58	$184.60	$184.60
Purchase #3	$240.37	7.665%	$258.7944	$258.79	$258.80	$258.80
Purchase #4	$101.93	7.674%	$109.7521	$109.75	$109.75	$109.80
Purchase #5	$59.48	13.116%	$67.2814	$67.28	$67.30	$67.30
Purchase #6	$121.38	5.221%	$127.7172	$127.72	$127.70	$127.70
Purchase #7	$6.38	13.208%	$7.2227	$7.22	$7.20	$7.20
7 purchase totals =	$738.87		$791.9516	$791.94	$791.95	$792.00