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	$126.48	3.810%	$131.2989	$131.30	$131.30	$131.30
Purchase #2	$237.30	7.600%	$255.3348	$255.33	$255.35	$255.30
Purchase #3	$6.89	11.821%	$7.7045	$7.70	$7.70	$7.70
Purchase #4	$125.53	12.742%	$141.525	$141.53	$141.55	$141.50
Purchase #5	$86.52	3.849%	$89.8502	$89.85	$89.85	$89.90
Purchase #6	$219.43	12.586%	$247.0475	$247.05	$247.05	$247.00
Purchase #7	$14.53	12.123%	$16.2915	$16.29	$16.30	$16.30
7 purchase totals =	$816.68		$889.0524	$889.05	$889.10	$889.00