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	6.134%	$264.6557	$264.66	$264.65	$264.70
Purchase #2	$28.72	12.143%	$32.2075	$32.21	$32.20	$32.20
Purchase #3	$222.56	12.374%	$250.0996	$250.10	$250.10	$250.10
Purchase #4	$102.79	13.661%	$116.8321	$116.83	$116.85	$116.80
Purchase #5	$200.47	10.127%	$220.7716	$220.77	$220.75	$220.80
Purchase #6	$136.40	12.412%	$153.33	$153.33	$153.35	$153.30
Purchase #7	$38.97	7.152%	$41.7571	$41.76	$41.75	$41.80
7 purchase totals =	$979.27		$1,079.6536	$1,079.66	$1,079.65	$1,079.70