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	$143.48	12.777%	$161.8124	$161.81	$161.80	$161.80
Purchase #2	$98.26	6.716%	$104.8591	$104.86	$104.85	$104.90
Purchase #3	$79.72	11.738%	$89.0775	$89.08	$89.10	$89.10
Purchase #4	$82.83	4.190%	$86.3006	$86.30	$86.30	$86.30
Purchase #5	$97.53	7.516%	$104.8604	$104.86	$104.85	$104.90
Purchase #6	$247.82	12.134%	$277.8905	$277.89	$277.90	$277.90
Purchase #7	$158.74	11.218%	$176.5475	$176.55	$176.55	$176.50
7 purchase totals =	$908.38		$1,001.3480	$1,001.35	$1,001.35	$1,001.40