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	$174.91	8.740%	$190.1971	$190.20	$190.20	$190.20
Purchase #2	$141.29	11.831%	$158.006	$158.01	$158.00	$158.00
Purchase #3	$160.67	5.198%	$169.0216	$169.02	$169.00	$169.00
Purchase #4	$78.42	11.448%	$87.3975	$87.40	$87.40	$87.40
Purchase #5	$127.96	6.660%	$136.4821	$136.48	$136.50	$136.50
Purchase #6	$15.55	11.300%	$17.3072	$17.31	$17.30	$17.30
Purchase #7	$72.97	10.834%	$80.8756	$80.88	$80.90	$80.90
7 purchase totals =	$771.77		$839.2871	$839.30	$839.30	$839.30