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	$121.33	13.638%	$137.877	$137.88	$137.90	$137.90
Purchase #2	$85.28	10.648%	$94.3606	$94.36	$94.35	$94.40
Purchase #3	$250.84	5.102%	$263.6379	$263.64	$263.65	$263.60
Purchase #4	$212.62	6.832%	$227.1462	$227.15	$227.15	$227.10
Purchase #5	$200.50	7.690%	$215.9185	$215.92	$215.90	$215.90
Purchase #6	$31.45	4.341%	$32.8152	$32.82	$32.80	$32.80
Purchase #7	$194.63	12.665%	$219.2799	$219.28	$219.30	$219.30
7 purchase totals =	$1,096.65		$1,191.0353	$1,191.05	$1,191.05	$1,191.00