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	$168.86	6.743%	$180.2462	$180.25	$180.25	$180.20
Purchase #2	$210.41	3.822%	$218.4519	$218.45	$218.45	$218.50
Purchase #3	$121.71	5.473%	$128.3712	$128.37	$128.35	$128.40
Purchase #4	$94.68	3.418%	$97.9162	$97.92	$97.90	$97.90
Purchase #5	$63.35	13.464%	$71.8794	$71.88	$71.90	$71.90
Purchase #6	$36.81	13.745%	$41.8695	$41.87	$41.85	$41.90
Purchase #7	$238.94	4.847%	$250.5214	$250.52	$250.50	$250.50
7 purchase totals =	$934.76		$989.2558	$989.26	$989.20	$989.30