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	$117.48	11.762%	$131.298	$131.30	$131.30	$131.30
Purchase #2	$198.89	11.627%	$222.0149	$222.01	$222.00	$222.00
Purchase #3	$151.89	4.489%	$158.7083	$158.71	$158.70	$158.70
Purchase #4	$63.44	5.536%	$66.952	$66.95	$66.95	$67.00
Purchase #5	$182.62	3.428%	$188.8802	$188.88	$188.90	$188.90
Purchase #6	$143.94	9.702%	$157.9051	$157.91	$157.90	$157.90
Purchase #7	$25.56	9.705%	$28.0406	$28.04	$28.05	$28.00
7 purchase totals =	$883.82		$953.7991	$953.80	$953.80	$953.80