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	$234.46	11.485%	$261.3877	$261.39	$261.40	$261.40
Purchase #2	$203.68	3.329%	$210.4605	$210.46	$210.45	$210.50
Purchase #3	$116.72	12.658%	$131.4944	$131.49	$131.50	$131.50
Purchase #4	$207.59	10.223%	$228.8119	$228.81	$228.80	$228.80
Purchase #5	$150.68	9.678%	$165.2628	$165.26	$165.25	$165.30
Purchase #6	$112.47	8.363%	$121.8759	$121.88	$121.90	$121.90
Purchase #7	$28.99	10.529%	$32.0424	$32.04	$32.05	$32.00
7 purchase totals =	$1,054.59		$1,151.3356	$1,151.33	$1,151.35	$1,151.40