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	$248.54	7.619%	$267.4763	$267.48	$267.50	$267.50
Purchase #2	$168.58	12.390%	$189.4671	$189.47	$189.45	$189.50
Purchase #3	$57.68	11.765%	$64.4661	$64.47	$64.45	$64.50
Purchase #4	$38.59	3.739%	$40.0329	$40.03	$40.05	$40.00
Purchase #5	$62.82	4.488%	$65.6394	$65.64	$65.65	$65.60
Purchase #6	$126.44	12.359%	$142.0667	$142.07	$142.05	$142.10
Purchase #7	$135.41	12.404%	$152.2063	$152.21	$152.20	$152.20
7 purchase totals =	$838.06		$921.3548	$921.37	$921.35	$921.40