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	$10.48	3.250%	$10.8206	$10.82	$10.80	$10.80
Purchase #2	$208.38	3.524%	$215.7233	$215.72	$215.70	$215.70
Purchase #3	$97.55	3.480%	$100.9447	$100.94	$100.95	$100.90
Purchase #4	$136.50	7.827%	$147.1839	$147.18	$147.20	$147.20
Purchase #5	$217.66	6.510%	$231.8297	$231.83	$231.85	$231.80
Purchase #6	$58.66	7.193%	$62.8794	$62.88	$62.90	$62.90
Purchase #7	$110.63	4.443%	$115.5453	$115.55	$115.55	$115.50
7 purchase totals =	$839.86		$884.9269	$884.92	$884.95	$884.80