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	$117.30	6.577%	$125.0148	$125.01	$125.00	$125.00
Purchase #2	$166.28	13.780%	$189.1934	$189.19	$189.20	$189.20
Purchase #3	$139.91	7.274%	$150.0871	$150.09	$150.10	$150.10
Purchase #4	$103.69	9.801%	$113.8527	$113.85	$113.85	$113.90
Purchase #5	$54.61	12.725%	$61.5591	$61.56	$61.55	$61.60
Purchase #6	$19.56	9.807%	$21.4782	$21.48	$21.50	$21.50
Purchase #7	$164.62	9.231%	$179.8161	$179.82	$179.80	$179.80
7 purchase totals =	$765.97		$841.0014	$841.00	$841.00	$841.10