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	$19.31	11.330%	$21.4978	$21.50	$21.50	$21.50
Purchase #2	$196.32	11.347%	$218.5964	$218.60	$218.60	$218.60
Purchase #3	$237.90	5.285%	$250.473	$250.47	$250.45	$250.50
Purchase #4	$243.59	11.548%	$271.7198	$271.72	$271.70	$271.70
Purchase #5	$224.93	8.432%	$243.8961	$243.90	$243.90	$243.90
Purchase #6	$165.83	11.752%	$185.3183	$185.32	$185.30	$185.30
Purchase #7	$44.96	8.665%	$48.8558	$48.86	$48.85	$48.90
7 purchase totals =	$1,132.84		$1,240.3572	$1,240.37	$1,240.30	$1,240.40