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	$159.48	3.809%	$165.5546	$165.55	$165.55	$165.60
Purchase #2	$220.52	9.224%	$240.8608	$240.86	$240.85	$240.90
Purchase #3	$157.56	8.740%	$171.3307	$171.33	$171.35	$171.30
Purchase #4	$75.59	10.849%	$83.7908	$83.79	$83.80	$83.80
Purchase #5	$208.54	3.445%	$215.7242	$215.72	$215.70	$215.70
Purchase #6	$129.37	6.773%	$138.1322	$138.13	$138.15	$138.10
Purchase #7	$13.73	12.660%	$15.4682	$15.47	$15.45	$15.50
7 purchase totals =	$964.79		$1,030.8615	$1,030.85	$1,030.85	$1,030.90