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	$249.36	12.416%	$280.3205	$280.32	$280.30	$280.30
Purchase #2	$43.27	3.736%	$44.8866	$44.89	$44.90	$44.90
Purchase #3	$186.50	5.281%	$196.3491	$196.35	$196.35	$196.30
Purchase #4	$143.27	9.283%	$156.5698	$156.57	$156.55	$156.60
Purchase #5	$238.86	11.309%	$265.8727	$265.87	$265.85	$265.90
Purchase #6	$86.97	13.856%	$99.0206	$99.02	$99.00	$99.00
Purchase #7	$86.31	5.855%	$91.3635	$91.36	$91.35	$91.40
7 purchase totals =	$1,034.54		$1,134.3828	$1,134.38	$1,134.30	$1,134.40