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	$25.25	12.592%	$28.4295	$28.43	$28.45	$28.40
Purchase #2	$187.59	4.487%	$196.0072	$196.01	$196.00	$196.00
Purchase #3	$71.88	5.490%	$75.8262	$75.83	$75.85	$75.80
Purchase #4	$69.25	4.440%	$72.3247	$72.32	$72.30	$72.30
Purchase #5	$49.25	6.489%	$52.4458	$52.45	$52.45	$52.40
Purchase #6	$16.75	12.692%	$18.8759	$18.88	$18.90	$18.90
Purchase #7	$135.52	8.705%	$147.317	$147.32	$147.30	$147.30
7 purchase totals =	$555.49		$591.2263	$591.24	$591.25	$591.10