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	$36.35	9.426%	$39.7764	$39.78	$39.80	$39.80
Purchase #2	$113.84	6.182%	$120.8776	$120.88	$120.90	$120.90
Purchase #3	$138.27	13.662%	$157.1604	$157.16	$157.15	$157.20
Purchase #4	$79.72	12.268%	$89.5	$89.50	$89.50	$89.50
Purchase #5	$39.95	12.698%	$45.0229	$45.02	$45.00	$45.00
Purchase #6	$126.44	11.626%	$141.1399	$141.14	$141.15	$141.10
Purchase #7	$249.84	6.261%	$265.4825	$265.48	$265.50	$265.50
7 purchase totals =	$784.41		$858.9597	$858.96	$859.00	$859.00