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	$150.63	9.741%	$165.3029	$165.30	$165.30	$165.30
Purchase #2	$123.91	10.389%	$136.783	$136.78	$136.80	$136.80
Purchase #3	$45.62	10.396%	$50.3627	$50.36	$50.35	$50.40
Purchase #4	$85.30	6.213%	$90.5997	$90.60	$90.60	$90.60
Purchase #5	$242.50	8.417%	$262.9112	$262.91	$262.90	$262.90
Purchase #6	$232.43	10.355%	$256.4981	$256.50	$256.50	$256.50
Purchase #7	$90.63	7.577%	$97.497	$97.50	$97.50	$97.50
7 purchase totals =	$971.02		$1,059.9546	$1,059.95	$1,059.95	$1,060.00