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	$5.96	13.276%	$6.7512	$6.75	$6.75	$6.80
Purchase #2	$188.50	5.219%	$198.3378	$198.34	$198.35	$198.30
Purchase #3	$173.46	13.252%	$196.4469	$196.45	$196.45	$196.40
Purchase #4	$212.48	3.204%	$219.2879	$219.29	$219.30	$219.30
Purchase #5	$156.94	13.441%	$178.0343	$178.03	$178.05	$178.00
Purchase #6	$42.96	8.123%	$46.4496	$46.45	$46.45	$46.40
Purchase #7	$238.41	4.604%	$249.3864	$249.39	$249.40	$249.40
7 purchase totals =	$1,018.71		$1,094.6941	$1,094.70	$1,094.75	$1,094.60