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	$38.33	5.808%	$40.5562	$40.56	$40.55	$40.60
Purchase #2	$201.25	5.655%	$212.6307	$212.63	$212.65	$212.60
Purchase #3	$63.94	4.845%	$67.0379	$67.04	$67.05	$67.00
Purchase #4	$124.47	13.344%	$141.0793	$141.08	$141.10	$141.10
Purchase #5	$199.36	13.265%	$225.8051	$225.81	$225.80	$225.80
Purchase #6	$94.31	5.405%	$99.4075	$99.41	$99.40	$99.40
Purchase #7	$147.65	3.366%	$152.6199	$152.62	$152.60	$152.60
7 purchase totals =	$869.31		$939.1366	$939.15	$939.15	$939.10