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	$80.45	13.427%	$91.252	$91.25	$91.25	$91.30
Purchase #2	$31.90	4.245%	$33.2542	$33.25	$33.25	$33.30
Purchase #3	$239.80	12.523%	$269.8302	$269.83	$269.85	$269.80
Purchase #4	$31.50	10.394%	$34.7741	$34.77	$34.75	$34.80
Purchase #5	$164.74	4.122%	$171.5306	$171.53	$171.55	$171.50
Purchase #6	$54.80	4.564%	$57.3011	$57.30	$57.30	$57.30
Purchase #7	$157.52	13.611%	$178.96	$178.96	$178.95	$179.00
7 purchase totals =	$760.71		$836.9022	$836.89	$836.90	$837.00