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	$58.27	11.315%	$64.8633	$64.86	$64.85	$64.90
Purchase #2	$134.47	4.261%	$140.1998	$140.20	$140.20	$140.20
Purchase #3	$142.57	4.458%	$148.9258	$148.93	$148.95	$148.90
Purchase #4	$222.80	13.713%	$253.3526	$253.35	$253.35	$253.40
Purchase #5	$128.62	10.391%	$141.9849	$141.98	$142.00	$142.00
Purchase #6	$37.52	13.230%	$42.4839	$42.48	$42.50	$42.50
Purchase #7	$191.62	10.715%	$212.1521	$212.15	$212.15	$212.20
7 purchase totals =	$915.87		$1,003.9624	$1,003.95	$1,004.00	$1,004.10