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	$222.35	9.767%	$244.0669	$244.07	$244.05	$244.10
Purchase #2	$83.52	7.275%	$89.5961	$89.60	$89.60	$89.60
Purchase #3	$30.59	3.171%	$31.56	$31.56	$31.55	$31.60
Purchase #4	$100.83	12.410%	$113.343	$113.34	$113.35	$113.30
Purchase #5	$227.48	5.846%	$240.7785	$240.78	$240.80	$240.80
Purchase #6	$21.63	12.777%	$24.3937	$24.39	$24.40	$24.40
Purchase #7	$89.70	7.456%	$96.388	$96.39	$96.40	$96.40
7 purchase totals =	$776.10		$840.1262	$840.13	$840.15	$840.20