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	$66.65	5.587%	$70.3737	$70.37	$70.35	$70.40
Purchase #2	$82.55	8.803%	$89.8169	$89.82	$89.80	$89.80
Purchase #3	$104.78	8.465%	$113.6496	$113.65	$113.65	$113.60
Purchase #4	$167.73	4.449%	$175.1923	$175.19	$175.20	$175.20
Purchase #5	$134.49	4.180%	$140.1117	$140.11	$140.10	$140.10
Purchase #6	$99.66	5.714%	$105.3546	$105.35	$105.35	$105.40
Purchase #7	$204.39	7.184%	$219.0734	$219.07	$219.05	$219.10
7 purchase totals =	$860.25		$913.5722	$913.56	$913.50	$913.60