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	$51.82	10.398%	$57.2082	$57.21	$57.20	$57.20
Purchase #2	$104.55	4.781%	$109.5485	$109.55	$109.55	$109.50
Purchase #3	$54.55	6.144%	$57.9016	$57.90	$57.90	$57.90
Purchase #4	$117.86	11.830%	$131.8028	$131.80	$131.80	$131.80
Purchase #5	$207.25	6.275%	$220.2549	$220.25	$220.25	$220.30
Purchase #6	$129.41	6.139%	$137.3545	$137.35	$137.35	$137.40
Purchase #7	$198.54	13.373%	$225.0908	$225.09	$225.10	$225.10
7 purchase totals =	$863.98		$939.1613	$939.15	$939.15	$939.20