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	$53.86	9.632%	$59.0478	$59.05	$59.05	$59.00
Purchase #2	$39.80	3.665%	$41.2587	$41.26	$41.25	$41.30
Purchase #3	$104.29	11.241%	$116.0132	$116.01	$116.00	$116.00
Purchase #4	$181.93	7.634%	$195.8185	$195.82	$195.80	$195.80
Purchase #5	$63.86	12.623%	$71.921	$71.92	$71.90	$71.90
Purchase #6	$58.79	3.536%	$60.8688	$60.87	$60.85	$60.90
Purchase #7	$144.44	10.800%	$160.0395	$160.04	$160.05	$160.00
7 purchase totals =	$646.97		$704.9675	$704.97	$704.90	$704.90