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	$39.34	6.298%	$41.8176	$41.82	$41.80	$41.80
Purchase #2	$122.76	13.504%	$139.3375	$139.34	$139.35	$139.30
Purchase #3	$57.84	12.298%	$64.9532	$64.95	$64.95	$65.00
Purchase #4	$41.86	9.223%	$45.7207	$45.72	$45.70	$45.70
Purchase #5	$185.31	12.550%	$208.5664	$208.57	$208.55	$208.60
Purchase #6	$27.81	5.395%	$29.3103	$29.31	$29.30	$29.30
Purchase #7	$63.82	3.129%	$65.8169	$65.82	$65.80	$65.80
7 purchase totals =	$538.74		$595.5226	$595.53	$595.45	$595.50