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	$99.34	3.146%	$102.4652	$102.47	$102.45	$102.50
Purchase #2	$202.89	3.184%	$209.35	$209.35	$209.35	$209.40
Purchase #3	$51.52	12.423%	$57.9203	$57.92	$57.90	$57.90
Purchase #4	$50.79	13.835%	$57.8168	$57.82	$57.80	$57.80
Purchase #5	$6.98	13.518%	$7.9236	$7.92	$7.90	$7.90
Purchase #6	$180.87	3.706%	$187.573	$187.57	$187.55	$187.60
Purchase #7	$139.33	11.678%	$155.601	$155.60	$155.60	$155.60
7 purchase totals =	$731.72		$778.6499	$778.65	$778.55	$778.70