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	$25.93	6.191%	$27.5353	$27.54	$27.55	$27.50
Purchase #2	$247.57	13.452%	$280.8731	$280.87	$280.85	$280.90
Purchase #3	$227.48	12.816%	$256.6338	$256.63	$256.65	$256.60
Purchase #4	$168.44	8.517%	$182.786	$182.79	$182.80	$182.80
Purchase #5	$85.93	5.566%	$90.7129	$90.71	$90.70	$90.70
Purchase #6	$80.26	3.852%	$83.3516	$83.35	$83.35	$83.40
Purchase #7	$196.98	4.230%	$205.3123	$205.31	$205.30	$205.30
7 purchase totals =	$1,032.59		$1,127.2050	$1,127.20	$1,127.20	$1,127.20