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	$90.38	4.473%	$94.4227	$94.42	$94.40	$94.40
Purchase #2	$80.34	12.735%	$90.5713	$90.57	$90.55	$90.60
Purchase #3	$38.86	9.586%	$42.5851	$42.59	$42.60	$42.60
Purchase #4	$98.97	13.402%	$112.234	$112.23	$112.25	$112.20
Purchase #5	$29.71	13.432%	$33.7006	$33.70	$33.70	$33.70
Purchase #6	$195.58	6.181%	$207.6688	$207.67	$207.65	$207.70
Purchase #7	$187.52	11.677%	$209.4167	$209.42	$209.40	$209.40
7 purchase totals =	$721.36		$790.5992	$790.60	$790.55	$790.60