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	$57.72	3.661%	$59.8331	$59.83	$59.85	$59.80
Purchase #2	$135.66	10.744%	$150.2353	$150.24	$150.25	$150.20
Purchase #3	$35.73	6.567%	$38.0764	$38.08	$38.10	$38.10
Purchase #4	$138.30	11.749%	$154.5489	$154.55	$154.55	$154.50
Purchase #5	$102.89	12.649%	$115.9046	$115.90	$115.90	$115.90
Purchase #6	$40.62	5.705%	$42.9374	$42.94	$42.95	$42.90
Purchase #7	$105.37	4.227%	$109.824	$109.82	$109.80	$109.80
7 purchase totals =	$616.29		$671.3597	$671.36	$671.40	$671.20