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	$104.64	11.846%	$117.0357	$117.04	$117.05	$117.00
Purchase #2	$190.95	4.850%	$200.2111	$200.21	$200.20	$200.20
Purchase #3	$34.68	11.868%	$38.7958	$38.80	$38.80	$38.80
Purchase #4	$213.27	12.525%	$239.9821	$239.98	$240.00	$240.00
Purchase #5	$176.90	12.546%	$199.0939	$199.09	$199.10	$199.10
Purchase #6	$147.73	3.304%	$152.611	$152.61	$152.60	$152.60
Purchase #7	$39.72	7.112%	$42.5449	$42.54	$42.55	$42.50
7 purchase totals =	$907.89		$990.2745	$990.27	$990.30	$990.20