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	$243.46	12.583%	$274.0946	$274.09	$274.10	$274.10
Purchase #2	$27.37	3.661%	$28.372	$28.37	$28.35	$28.40
Purchase #3	$189.79	9.779%	$208.3496	$208.35	$208.35	$208.30
Purchase #4	$84.55	6.440%	$89.995	$90.00	$90.00	$90.00
Purchase #5	$188.66	4.306%	$196.7837	$196.78	$196.80	$196.80
Purchase #6	$136.92	10.342%	$151.0803	$151.08	$151.10	$151.10
Purchase #7	$135.26	13.754%	$153.8637	$153.86	$153.85	$153.90
7 purchase totals =	$1,006.01		$1,102.5389	$1,102.53	$1,102.55	$1,102.60