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	$203.76	6.279%	$216.5541	$216.55	$216.55	$216.60
Purchase #2	$79.73	5.167%	$83.8496	$83.85	$83.85	$83.80
Purchase #3	$133.98	4.384%	$139.8537	$139.85	$139.85	$139.90
Purchase #4	$240.34	12.765%	$271.0194	$271.02	$271.00	$271.00
Purchase #5	$59.48	11.720%	$66.4511	$66.45	$66.45	$66.50
Purchase #6	$81.96	5.449%	$86.426	$86.43	$86.45	$86.40
Purchase #7	$38.63	8.662%	$41.9761	$41.98	$42.00	$42.00
7 purchase totals =	$837.88		$906.1300	$906.13	$906.15	$906.20