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	$29.93	6.220%	$31.7916	$31.79	$31.80	$31.80
Purchase #2	$169.30	5.595%	$178.7723	$178.77	$178.75	$178.80
Purchase #3	$82.63	7.719%	$89.0082	$89.01	$89.00	$89.00
Purchase #4	$172.50	5.823%	$182.5447	$182.54	$182.55	$182.50
Purchase #5	$201.66	11.522%	$224.8953	$224.90	$224.90	$224.90
Purchase #6	$57.59	9.287%	$62.9384	$62.94	$62.95	$62.90
Purchase #7	$64.49	4.314%	$67.2721	$67.27	$67.25	$67.30
7 purchase totals =	$778.10		$837.2226	$837.22	$837.20	$837.20