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	$181.69	11.865%	$203.2475	$203.25	$203.25	$203.20
Purchase #2	$33.40	6.188%	$35.4668	$35.47	$35.45	$35.50
Purchase #3	$62.56	13.749%	$71.1614	$71.16	$71.15	$71.20
Purchase #4	$73.90	9.577%	$80.9774	$80.98	$81.00	$81.00
Purchase #5	$51.34	4.792%	$53.8002	$53.80	$53.80	$53.80
Purchase #6	$25.88	5.456%	$27.292	$27.29	$27.30	$27.30
Purchase #7	$111.98	13.853%	$127.4926	$127.49	$127.50	$127.50
7 purchase totals =	$540.75		$599.4379	$599.44	$599.45	$599.50