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	$37.55	12.474%	$42.234	$42.23	$42.25	$42.20
Purchase #2	$138.27	13.431%	$156.841	$156.84	$156.85	$156.80
Purchase #3	$96.45	6.455%	$102.6758	$102.68	$102.70	$102.70
Purchase #4	$61.82	6.833%	$66.0442	$66.04	$66.05	$66.00
Purchase #5	$187.55	5.765%	$198.3623	$198.36	$198.35	$198.40
Purchase #6	$61.90	8.159%	$66.9504	$66.95	$66.95	$67.00
Purchase #7	$68.79	4.727%	$72.0417	$72.04	$72.05	$72.00
7 purchase totals =	$652.33		$705.1494	$705.14	$705.20	$705.10