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	$38.42	7.563%	$41.3257	$41.33	$41.35	$41.30
Purchase #2	$222.50	7.815%	$239.8884	$239.89	$239.90	$239.90
Purchase #3	$12.88	11.559%	$14.3688	$14.37	$14.35	$14.40
Purchase #4	$58.50	6.593%	$62.3569	$62.36	$62.35	$62.40
Purchase #5	$116.59	12.516%	$131.1824	$131.18	$131.20	$131.20
Purchase #6	$242.38	12.670%	$273.0895	$273.09	$273.10	$273.10
Purchase #7	$61.87	9.128%	$67.5175	$67.52	$67.50	$67.50
7 purchase totals =	$753.14		$829.7292	$829.74	$829.75	$829.80