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	$131.90	5.479%	$139.1268	$139.13	$139.15	$139.10
Purchase #2	$49.58	7.433%	$53.2653	$53.27	$53.25	$53.30
Purchase #3	$232.79	12.110%	$260.9809	$260.98	$261.00	$261.00
Purchase #4	$223.50	4.478%	$233.5083	$233.51	$233.50	$233.50
Purchase #5	$164.25	13.510%	$186.4402	$186.44	$186.45	$186.40
Purchase #6	$78.66	13.334%	$89.1485	$89.15	$89.15	$89.10
Purchase #7	$225.88	7.694%	$243.2592	$243.26	$243.25	$243.30
7 purchase totals =	$1,106.56		$1,205.7292	$1,205.74	$1,205.75	$1,205.70