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	$106.26	3.340%	$109.8091	$109.81	$109.80	$109.80
Purchase #2	$52.52	4.749%	$55.0142	$55.01	$55.00	$55.00
Purchase #3	$215.76	3.799%	$223.9567	$223.96	$223.95	$224.00
Purchase #4	$242.54	6.356%	$257.9558	$257.96	$257.95	$258.00
Purchase #5	$128.56	10.324%	$141.8325	$141.83	$141.85	$141.80
Purchase #6	$209.94	4.405%	$219.1879	$219.19	$219.20	$219.20
Purchase #7	$64.51	12.455%	$72.5447	$72.54	$72.55	$72.50
7 purchase totals =	$1,020.09		$1,080.3009	$1,080.30	$1,080.30	$1,080.30