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	$23.56	10.251%	$25.9751	$25.98	$26.00	$26.00
Purchase #2	$41.28	4.412%	$43.1013	$43.10	$43.10	$43.10
Purchase #3	$132.63	13.520%	$150.5616	$150.56	$150.55	$150.60
Purchase #4	$162.91	13.839%	$185.4551	$185.46	$185.45	$185.50
Purchase #5	$126.46	5.296%	$133.1573	$133.16	$133.15	$133.20
Purchase #6	$238.57	12.523%	$268.4461	$268.45	$268.45	$268.40
Purchase #7	$219.55	6.293%	$233.3663	$233.37	$233.35	$233.40
7 purchase totals =	$944.96		$1,040.0628	$1,040.08	$1,040.05	$1,040.20