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	$46.50	13.803%	$52.9184	$52.92	$52.90	$52.90
Purchase #2	$127.89	7.424%	$137.3846	$137.38	$137.40	$137.40
Purchase #3	$192.53	12.804%	$217.1815	$217.18	$217.20	$217.20
Purchase #4	$203.46	8.802%	$221.3685	$221.37	$221.35	$221.40
Purchase #5	$38.63	4.166%	$40.2393	$40.24	$40.25	$40.20
Purchase #6	$65.60	10.296%	$72.3542	$72.35	$72.35	$72.40
Purchase #7	$68.67	4.433%	$71.7141	$71.71	$71.70	$71.70
7 purchase totals =	$743.28		$813.1606	$813.15	$813.15	$813.20