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	$116.89	5.779%	$123.6451	$123.65	$123.65	$123.60
Purchase #2	$151.88	7.106%	$162.6726	$162.67	$162.65	$162.70
Purchase #3	$78.61	13.134%	$88.9346	$88.93	$88.95	$88.90
Purchase #4	$69.50	10.315%	$76.6689	$76.67	$76.65	$76.70
Purchase #5	$127.47	8.497%	$138.3011	$138.30	$138.30	$138.30
Purchase #6	$137.73	3.598%	$142.6855	$142.69	$142.70	$142.70
Purchase #7	$167.75	12.343%	$188.4554	$188.46	$188.45	$188.50
7 purchase totals =	$849.83		$921.3632	$921.37	$921.35	$921.40