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	$65.49	4.682%	$68.5562	$68.56	$68.55	$68.60
Purchase #2	$18.63	9.521%	$20.4038	$20.40	$20.40	$20.40
Purchase #3	$229.78	6.765%	$245.3246	$245.32	$245.30	$245.30
Purchase #4	$144.50	8.199%	$156.3476	$156.35	$156.35	$156.30
Purchase #5	$24.62	12.304%	$27.6492	$27.65	$27.65	$27.60
Purchase #6	$139.53	8.544%	$151.4514	$151.45	$151.45	$151.50
Purchase #7	$180.62	5.645%	$190.816	$190.82	$190.80	$190.80
7 purchase totals =	$803.17		$860.5488	$860.55	$860.50	$860.50