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	$50.78	9.466%	$55.5868	$55.59	$55.60	$55.60
Purchase #2	$18.80	6.620%	$20.0446	$20.04	$20.05	$20.00
Purchase #3	$186.88	11.279%	$207.9582	$207.96	$207.95	$208.00
Purchase #4	$55.85	6.140%	$59.2792	$59.28	$59.30	$59.30
Purchase #5	$94.43	6.564%	$100.6284	$100.63	$100.65	$100.60
Purchase #6	$55.61	11.570%	$62.0441	$62.04	$62.05	$62.00
Purchase #7	$63.50	6.568%	$67.6707	$67.67	$67.65	$67.70
7 purchase totals =	$525.85		$573.2120	$573.21	$573.25	$573.20