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	$34.81	9.258%	$38.0327	$38.03	$38.05	$38.00
Purchase #2	$164.43	11.427%	$183.2194	$183.22	$183.20	$183.20
Purchase #3	$198.25	8.456%	$215.014	$215.01	$215.00	$215.00
Purchase #4	$6.31	6.303%	$6.7077	$6.71	$6.70	$6.70
Purchase #5	$53.90	11.123%	$59.8953	$59.90	$59.90	$59.90
Purchase #6	$227.48	6.666%	$242.6438	$242.64	$242.65	$242.60
Purchase #7	$142.59	6.360%	$151.6587	$151.66	$151.65	$151.70
7 purchase totals =	$827.77		$897.1716	$897.17	$897.15	$897.10