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	$37.78	12.324%	$42.436	$42.44	$42.45	$42.40
Purchase #2	$186.34	9.829%	$204.6554	$204.66	$204.65	$204.70
Purchase #3	$18.78	9.220%	$20.5115	$20.51	$20.50	$20.50
Purchase #4	$217.76	11.740%	$243.325	$243.33	$243.35	$243.30
Purchase #5	$139.57	3.559%	$144.5373	$144.54	$144.55	$144.50
Purchase #6	$114.49	8.127%	$123.7946	$123.79	$123.80	$123.80
Purchase #7	$140.62	9.511%	$153.9944	$153.99	$154.00	$154.00
7 purchase totals =	$855.34		$933.2542	$933.26	$933.30	$933.20