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	$57.70	11.711%	$64.4572	$64.46	$64.45	$64.50
Purchase #2	$119.88	7.512%	$128.8854	$128.89	$128.90	$128.90
Purchase #3	$162.32	3.676%	$168.2869	$168.29	$168.30	$168.30
Purchase #4	$136.68	3.119%	$140.943	$140.94	$140.95	$140.90
Purchase #5	$51.97	7.156%	$55.689	$55.69	$55.70	$55.70
Purchase #6	$35.46	11.501%	$39.5383	$39.54	$39.55	$39.50
Purchase #7	$11.47	5.847%	$12.1407	$12.14	$12.15	$12.10
7 purchase totals =	$575.48		$609.9405	$609.95	$610.00	$609.90