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	$59.81	13.827%	$68.0799	$68.08	$68.10	$68.10
Purchase #2	$112.51	9.428%	$123.1174	$123.12	$123.10	$123.10
Purchase #3	$188.29	11.283%	$209.5348	$209.53	$209.55	$209.50
Purchase #4	$249.75	13.834%	$284.3004	$284.30	$284.30	$284.30
Purchase #5	$39.31	6.568%	$41.8919	$41.89	$41.90	$41.90
Purchase #6	$56.37	5.396%	$59.4117	$59.41	$59.40	$59.40
Purchase #7	$35.96	12.225%	$40.3561	$40.36	$40.35	$40.40
7 purchase totals =	$742.00		$826.6922	$826.69	$826.70	$826.70