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	$160.98	10.575%	$178.0036	$178.00	$178.00	$178.00
Purchase #2	$94.71	4.874%	$99.3262	$99.33	$99.35	$99.30
Purchase #3	$228.54	13.254%	$258.8307	$258.83	$258.85	$258.80
Purchase #4	$136.58	11.853%	$152.7688	$152.77	$152.75	$152.80
Purchase #5	$177.82	8.473%	$192.8867	$192.89	$192.90	$192.90
Purchase #6	$241.76	8.171%	$261.5142	$261.51	$261.50	$261.50
Purchase #7	$37.26	3.511%	$38.5682	$38.57	$38.55	$38.60
7 purchase totals =	$1,077.65		$1,181.8984	$1,181.90	$1,181.90	$1,181.90