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	$60.85	4.317%	$63.4769	$63.48	$63.50	$63.50
Purchase #2	$122.38	12.651%	$137.8623	$137.86	$137.85	$137.90
Purchase #3	$97.25	4.753%	$101.8723	$101.87	$101.85	$101.90
Purchase #4	$41.97	9.195%	$45.8291	$45.83	$45.85	$45.80
Purchase #5	$125.75	4.836%	$131.8313	$131.83	$131.85	$131.80
Purchase #6	$238.61	13.734%	$271.3807	$271.38	$271.40	$271.40
Purchase #7	$76.46	11.611%	$85.3378	$85.34	$85.35	$85.30
7 purchase totals =	$763.27		$837.5904	$837.59	$837.65	$837.60