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	$41.50	10.534%	$45.8716	$45.87	$45.85	$45.90
Purchase #2	$156.63	11.363%	$174.4279	$174.43	$174.45	$174.40
Purchase #3	$232.27	12.583%	$261.4965	$261.50	$261.50	$261.50
Purchase #4	$86.78	10.455%	$95.8528	$95.85	$95.85	$95.90
Purchase #5	$243.93	10.259%	$268.9548	$268.95	$268.95	$269.00
Purchase #6	$39.49	7.224%	$42.3428	$42.34	$42.35	$42.30
Purchase #7	$179.86	12.391%	$202.1465	$202.15	$202.15	$202.10
7 purchase totals =	$980.46		$1,091.0929	$1,091.09	$1,091.10	$1,091.10