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	$43.70	8.793%	$47.5425	$47.54	$47.55	$47.50
Purchase #2	$94.89	10.160%	$104.5308	$104.53	$104.55	$104.50
Purchase #3	$84.49	12.222%	$94.8164	$94.82	$94.80	$94.80
Purchase #4	$118.67	10.843%	$131.5374	$131.54	$131.55	$131.50
Purchase #5	$12.70	13.652%	$14.4338	$14.43	$14.45	$14.40
Purchase #6	$142.54	12.869%	$160.8835	$160.88	$160.90	$160.90
Purchase #7	$239.61	9.464%	$262.2867	$262.29	$262.30	$262.30
7 purchase totals =	$736.60		$816.0311	$816.03	$816.10	$815.90