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	$248.98	12.588%	$280.3216	$280.32	$280.30	$280.30
Purchase #2	$25.29	9.350%	$27.6546	$27.65	$27.65	$27.70
Purchase #3	$162.36	8.185%	$175.6492	$175.65	$175.65	$175.60
Purchase #4	$203.56	4.531%	$212.7833	$212.78	$212.80	$212.80
Purchase #5	$204.78	4.123%	$213.2231	$213.22	$213.20	$213.20
Purchase #6	$84.26	5.842%	$89.1825	$89.18	$89.20	$89.20
Purchase #7	$187.54	5.639%	$198.1154	$198.12	$198.10	$198.10
7 purchase totals =	$1,116.77		$1,196.9297	$1,196.92	$1,196.90	$1,196.90