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	$94.37	11.823%	$105.5274	$105.53	$105.55	$105.50
Purchase #2	$111.72	6.725%	$119.2332	$119.23	$119.25	$119.20
Purchase #3	$239.72	7.666%	$258.0969	$258.10	$258.10	$258.10
Purchase #4	$109.26	10.776%	$121.0339	$121.03	$121.05	$121.00
Purchase #5	$158.69	13.360%	$179.891	$179.89	$179.90	$179.90
Purchase #6	$7.35	13.133%	$8.3153	$8.32	$8.30	$8.30
Purchase #7	$53.55	11.134%	$59.5123	$59.51	$59.50	$59.50
7 purchase totals =	$774.66		$851.6100	$851.61	$851.65	$851.50