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	$177.31	6.601%	$189.0142	$189.01	$189.00	$189.00
Purchase #2	$123.31	8.566%	$133.8727	$133.87	$133.85	$133.90
Purchase #3	$242.73	13.380%	$275.2073	$275.21	$275.20	$275.20
Purchase #4	$249.65	12.514%	$280.8912	$280.89	$280.90	$280.90
Purchase #5	$187.87	10.720%	$208.0097	$208.01	$208.00	$208.00
Purchase #6	$82.89	7.776%	$89.3355	$89.34	$89.35	$89.30
Purchase #7	$197.41	7.323%	$211.8663	$211.87	$211.85	$211.90
7 purchase totals =	$1,261.17		$1,388.1969	$1,388.20	$1,388.15	$1,388.20