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	$175.88	7.642%	$189.3207	$189.32	$189.30	$189.30
Purchase #2	$106.42	11.286%	$118.4306	$118.43	$118.45	$118.40
Purchase #3	$197.70	13.249%	$223.8933	$223.89	$223.90	$223.90
Purchase #4	$150.30	11.581%	$167.7062	$167.71	$167.70	$167.70
Purchase #5	$118.79	3.869%	$123.386	$123.39	$123.40	$123.40
Purchase #6	$59.48	12.456%	$66.8888	$66.89	$66.90	$66.90
Purchase #7	$116.96	6.215%	$124.2291	$124.23	$124.25	$124.20
7 purchase totals =	$925.53		$1,013.8547	$1,013.86	$1,013.90	$1,013.80