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	$28.94	7.755%	$31.1843	$31.18	$31.20	$31.20
Purchase #2	$203.26	6.751%	$216.9821	$216.98	$217.00	$217.00
Purchase #3	$88.52	11.734%	$98.9069	$98.91	$98.90	$98.90
Purchase #4	$248.78	12.656%	$280.2656	$280.27	$280.25	$280.30
Purchase #5	$246.73	9.711%	$270.69	$270.69	$270.70	$270.70
Purchase #6	$72.28	8.855%	$78.6804	$78.68	$78.70	$78.70
Purchase #7	$38.28	12.820%	$43.1875	$43.19	$43.20	$43.20
7 purchase totals =	$926.79		$1,019.8968	$1,019.90	$1,019.95	$1,020.00