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	$15.70	12.646%	$17.6854	$17.69	$17.70	$17.70
Purchase #2	$222.33	9.363%	$243.1468	$243.15	$243.15	$243.10
Purchase #3	$70.33	12.173%	$78.8913	$78.89	$78.90	$78.90
Purchase #4	$51.46	8.181%	$55.6699	$55.67	$55.65	$55.70
Purchase #5	$105.61	12.863%	$119.1946	$119.19	$119.20	$119.20
Purchase #6	$50.90	9.130%	$55.5472	$55.55	$55.55	$55.50
Purchase #7	$35.77	5.418%	$37.708	$37.71	$37.70	$37.70
7 purchase totals =	$552.10		$607.8432	$607.85	$607.85	$607.80