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	$96.64	4.290%	$100.7859	$100.79	$100.80	$100.80
Purchase #2	$185.94	6.734%	$198.4612	$198.46	$198.45	$198.50
Purchase #3	$35.78	13.624%	$40.6547	$40.65	$40.65	$40.70
Purchase #4	$206.95	13.201%	$234.2695	$234.27	$234.25	$234.30
Purchase #5	$218.50	10.280%	$240.9618	$240.96	$240.95	$241.00
Purchase #6	$98.46	7.297%	$105.6446	$105.64	$105.65	$105.60
Purchase #7	$247.50	10.667%	$273.9008	$273.90	$273.90	$273.90
7 purchase totals =	$1,089.77		$1,194.6785	$1,194.67	$1,194.65	$1,194.80