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	$176.64	8.702%	$192.0112	$192.01	$192.00	$192.00
Purchase #2	$83.93	7.311%	$90.0661	$90.07	$90.05	$90.10
Purchase #3	$167.34	12.472%	$188.2106	$188.21	$188.20	$188.20
Purchase #4	$13.31	11.804%	$14.8811	$14.88	$14.90	$14.90
Purchase #5	$38.25	12.142%	$42.8943	$42.89	$42.90	$42.90
Purchase #6	$119.28	10.489%	$131.7913	$131.79	$131.80	$131.80
Purchase #7	$239.37	12.386%	$269.0184	$269.02	$269.00	$269.00
7 purchase totals =	$838.12		$928.8730	$928.87	$928.85	$928.90