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	$55.82	4.874%	$58.5407	$58.54	$58.55	$58.50
Purchase #2	$113.32	4.380%	$118.2834	$118.28	$118.30	$118.30
Purchase #3	$198.56	13.628%	$225.6198	$225.62	$225.60	$225.60
Purchase #4	$38.32	6.747%	$40.9055	$40.91	$40.90	$40.90
Purchase #5	$62.50	7.306%	$67.0663	$67.07	$67.05	$67.10
Purchase #6	$184.38	13.639%	$209.5276	$209.53	$209.55	$209.50
Purchase #7	$63.41	3.485%	$65.6198	$65.62	$65.60	$65.60
7 purchase totals =	$716.31		$785.5631	$785.57	$785.55	$785.50