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	$64.31	10.575%	$71.1108	$71.11	$71.10	$71.10
Purchase #2	$113.49	7.433%	$121.9257	$121.93	$121.95	$121.90
Purchase #3	$242.79	7.658%	$261.3829	$261.38	$261.40	$261.40
Purchase #4	$92.73	12.551%	$104.3685	$104.37	$104.35	$104.40
Purchase #5	$92.75	8.300%	$100.4483	$100.45	$100.45	$100.40
Purchase #6	$44.32	6.495%	$47.1986	$47.20	$47.20	$47.20
Purchase #7	$65.43	3.841%	$67.9432	$67.94	$67.95	$67.90
7 purchase totals =	$715.82		$774.3780	$774.38	$774.40	$774.30