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	$40.54	12.565%	$45.6339	$45.63	$45.65	$45.60
Purchase #2	$173.78	10.239%	$191.5733	$191.57	$191.55	$191.60
Purchase #3	$164.72	8.870%	$179.3307	$179.33	$179.35	$179.30
Purchase #4	$122.65	12.102%	$137.4931	$137.49	$137.50	$137.50
Purchase #5	$219.93	7.538%	$236.5083	$236.51	$236.50	$236.50
Purchase #6	$37.25	12.302%	$41.8325	$41.83	$41.85	$41.80
Purchase #7	$226.98	9.666%	$248.9199	$248.92	$248.90	$248.90
7 purchase totals =	$985.85		$1,081.2917	$1,081.28	$1,081.30	$1,081.20