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	$66.56	5.623%	$70.3027	$70.30	$70.30	$70.30
Purchase #2	$125.61	8.655%	$136.4815	$136.48	$136.50	$136.50
Purchase #3	$105.85	12.661%	$119.2517	$119.25	$119.25	$119.30
Purchase #4	$206.45	4.196%	$215.1126	$215.11	$215.10	$215.10
Purchase #5	$125.44	4.753%	$131.4022	$131.40	$131.40	$131.40
Purchase #6	$45.89	13.828%	$52.2357	$52.24	$52.25	$52.20
Purchase #7	$211.57	3.445%	$218.8586	$218.86	$218.85	$218.90
7 purchase totals =	$887.37		$943.6450	$943.64	$943.65	$943.70