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	$6.74	9.768%	$7.3984	$7.40	$7.40	$7.40
Purchase #2	$212.78	4.842%	$223.0828	$223.08	$223.10	$223.10
Purchase #3	$104.30	11.535%	$116.331	$116.33	$116.35	$116.30
Purchase #4	$185.84	5.559%	$196.1708	$196.17	$196.15	$196.20
Purchase #5	$231.54	12.736%	$261.0289	$261.03	$261.05	$261.00
Purchase #6	$181.34	9.763%	$199.0442	$199.04	$199.05	$199.00
Purchase #7	$111.94	13.833%	$127.4247	$127.42	$127.40	$127.40
7 purchase totals =	$1,034.48		$1,130.4808	$1,130.47	$1,130.50	$1,130.40