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	$29.66	7.187%	$31.7917	$31.79	$31.80	$31.80
Purchase #2	$56.29	11.724%	$62.8894	$62.89	$62.90	$62.90
Purchase #3	$222.83	10.378%	$245.9553	$245.96	$245.95	$246.00
Purchase #4	$168.63	8.682%	$183.2705	$183.27	$183.25	$183.30
Purchase #5	$55.38	12.162%	$62.1153	$62.12	$62.10	$62.10
Purchase #6	$146.91	4.824%	$153.9969	$154.00	$154.00	$154.00
Purchase #7	$175.78	11.668%	$196.29	$196.29	$196.30	$196.30
7 purchase totals =	$855.48		$936.3091	$936.32	$936.30	$936.40