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	$10.83	8.711%	$11.7734	$11.77	$11.75	$11.80
Purchase #2	$80.77	11.824%	$90.3202	$90.32	$90.30	$90.30
Purchase #3	$15.50	8.654%	$16.8414	$16.84	$16.85	$16.80
Purchase #4	$140.49	8.790%	$152.8391	$152.84	$152.85	$152.80
Purchase #5	$150.37	4.351%	$156.9126	$156.91	$156.90	$156.90
Purchase #6	$38.94	6.677%	$41.54	$41.54	$41.55	$41.50
Purchase #7	$107.83	12.650%	$121.4705	$121.47	$121.45	$121.50
7 purchase totals =	$544.73		$591.6972	$591.69	$591.65	$591.60