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	$115.66	12.565%	$130.1927	$130.19	$130.20	$130.20
Purchase #2	$56.38	5.389%	$59.4183	$59.42	$59.40	$59.40
Purchase #3	$116.92	9.747%	$128.3162	$128.32	$128.30	$128.30
Purchase #4	$38.94	12.716%	$43.8916	$43.89	$43.90	$43.90
Purchase #5	$131.30	9.696%	$144.0308	$144.03	$144.05	$144.00
Purchase #6	$223.89	8.677%	$243.3169	$243.32	$243.30	$243.30
Purchase #7	$157.71	13.711%	$179.3336	$179.33	$179.35	$179.30
7 purchase totals =	$840.80		$928.5001	$928.50	$928.50	$928.40