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	$36.49	6.443%	$38.8411	$38.84	$38.85	$38.80
Purchase #2	$33.45	13.157%	$37.851	$37.85	$37.85	$37.90
Purchase #3	$123.62	6.359%	$131.481	$131.48	$131.50	$131.50
Purchase #4	$188.32	8.142%	$203.653	$203.65	$203.65	$203.70
Purchase #5	$25.90	11.405%	$28.8539	$28.85	$28.85	$28.90
Purchase #6	$146.96	7.124%	$157.4294	$157.43	$157.45	$157.40
Purchase #7	$210.83	4.767%	$220.8803	$220.88	$220.90	$220.90
7 purchase totals =	$765.57		$818.9897	$818.98	$819.05	$819.10