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	$227.41	13.691%	$258.5447	$258.54	$258.55	$258.50
Purchase #2	$36.43	6.568%	$38.8227	$38.82	$38.80	$38.80
Purchase #3	$193.42	3.685%	$200.5475	$200.55	$200.55	$200.50
Purchase #4	$242.44	5.664%	$256.1718	$256.17	$256.15	$256.20
Purchase #5	$184.88	10.239%	$203.8099	$203.81	$203.80	$203.80
Purchase #6	$65.85	7.843%	$71.0146	$71.01	$71.00	$71.00
Purchase #7	$62.51	3.443%	$64.6622	$64.66	$64.65	$64.70
7 purchase totals =	$1,012.94		$1,093.5734	$1,093.56	$1,093.50	$1,093.50