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	$138.27	7.316%	$148.3858	$148.39	$148.40	$148.40
Purchase #2	$55.97	6.582%	$59.6539	$59.65	$59.65	$59.70
Purchase #3	$51.54	4.426%	$53.8212	$53.82	$53.80	$53.80
Purchase #4	$211.72	10.558%	$234.0734	$234.07	$234.05	$234.10
Purchase #5	$73.90	12.128%	$82.8626	$82.86	$82.85	$82.90
Purchase #6	$199.60	10.406%	$220.3704	$220.37	$220.35	$220.40
Purchase #7	$232.29	4.752%	$243.3284	$243.33	$243.35	$243.30
7 purchase totals =	$963.29		$1,042.4957	$1,042.49	$1,042.45	$1,042.60