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	$77.30	7.417%	$83.0333	$83.03	$83.05	$83.00
Purchase #2	$169.40	5.384%	$178.5205	$178.52	$178.50	$178.50
Purchase #3	$146.37	12.315%	$164.3955	$164.40	$164.40	$164.40
Purchase #4	$140.56	7.349%	$150.8898	$150.89	$150.90	$150.90
Purchase #5	$112.72	3.309%	$116.4499	$116.45	$116.45	$116.40
Purchase #6	$57.89	12.544%	$65.1517	$65.15	$65.15	$65.20
Purchase #7	$109.39	9.443%	$119.7197	$119.72	$119.70	$119.70
7 purchase totals =	$813.63		$878.1604	$878.16	$878.15	$878.10