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	$25.26	4.665%	$26.4384	$26.44	$26.45	$26.40
Purchase #2	$197.67	6.493%	$210.5047	$210.50	$210.50	$210.50
Purchase #3	$208.66	6.697%	$222.634	$222.63	$222.65	$222.60
Purchase #4	$72.44	7.826%	$78.1092	$78.11	$78.10	$78.10
Purchase #5	$28.83	10.515%	$31.8615	$31.86	$31.85	$31.90
Purchase #6	$46.76	13.419%	$53.0347	$53.03	$53.05	$53.00
Purchase #7	$11.83	4.348%	$12.3444	$12.34	$12.35	$12.30
7 purchase totals =	$591.45		$634.9269	$634.91	$634.95	$634.80