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	$48.51	13.865%	$55.2359	$55.24	$55.25	$55.20
Purchase #2	$138.47	8.701%	$150.5183	$150.52	$150.50	$150.50
Purchase #3	$186.83	12.165%	$209.5579	$209.56	$209.55	$209.60
Purchase #4	$249.82	3.629%	$258.886	$258.89	$258.90	$258.90
Purchase #5	$169.68	12.548%	$190.9714	$190.97	$190.95	$191.00
Purchase #6	$54.32	4.727%	$56.8877	$56.89	$56.90	$56.90
Purchase #7	$40.97	9.503%	$44.8634	$44.86	$44.85	$44.90
7 purchase totals =	$888.60		$966.9206	$966.93	$966.90	$967.00