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	$6.61	13.386%	$7.4948	$7.49	$7.50	$7.50
Purchase #2	$60.82	10.155%	$66.9963	$67.00	$67.00	$67.00
Purchase #3	$208.71	9.407%	$228.3433	$228.34	$228.35	$228.30
Purchase #4	$46.95	9.354%	$51.3417	$51.34	$51.35	$51.30
Purchase #5	$93.48	10.767%	$103.545	$103.55	$103.55	$103.50
Purchase #6	$12.85	5.339%	$13.5361	$13.54	$13.55	$13.50
Purchase #7	$31.88	12.537%	$35.8768	$35.88	$35.90	$35.90
7 purchase totals =	$461.30		$507.1340	$507.14	$507.20	$507.00