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	$216.55	10.318%	$238.8936	$238.89	$238.90	$238.90
Purchase #2	$78.59	6.137%	$83.4131	$83.41	$83.40	$83.40
Purchase #3	$120.65	8.687%	$131.1309	$131.13	$131.15	$131.10
Purchase #4	$49.34	3.798%	$51.2139	$51.21	$51.20	$51.20
Purchase #5	$165.90	9.709%	$182.0072	$182.01	$182.00	$182.00
Purchase #6	$81.34	12.290%	$91.3367	$91.34	$91.35	$91.30
Purchase #7	$128.59	6.363%	$136.7722	$136.77	$136.75	$136.80
7 purchase totals =	$840.96		$914.7676	$914.76	$914.75	$914.70