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	$36.78	10.680%	$40.7081	$40.71	$40.70	$40.70
Purchase #2	$119.57	4.715%	$125.2077	$125.21	$125.20	$125.20
Purchase #3	$139.67	10.580%	$154.4471	$154.45	$154.45	$154.40
Purchase #4	$225.38	12.560%	$253.6877	$253.69	$253.70	$253.70
Purchase #5	$213.37	3.856%	$221.5975	$221.60	$221.60	$221.60
Purchase #6	$39.56	7.127%	$42.3794	$42.38	$42.40	$42.40
Purchase #7	$151.85	10.199%	$167.3372	$167.34	$167.35	$167.30
7 purchase totals =	$926.18		$1,005.3647	$1,005.38	$1,005.40	$1,005.30