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	$102.28	3.633%	$105.9958	$106.00	$106.00	$106.00
Purchase #2	$208.30	3.493%	$215.5759	$215.58	$215.60	$215.60
Purchase #3	$62.94	6.443%	$66.9952	$67.00	$67.00	$67.00
Purchase #4	$127.97	7.467%	$137.5255	$137.53	$137.55	$137.50
Purchase #5	$203.48	6.704%	$217.1213	$217.12	$217.10	$217.10
Purchase #6	$69.34	4.582%	$72.5172	$72.52	$72.50	$72.50
Purchase #7	$85.46	6.214%	$90.7705	$90.77	$90.75	$90.80
7 purchase totals =	$859.77		$906.5014	$906.52	$906.50	$906.50