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	$214.45	12.270%	$240.763	$240.76	$240.75	$240.80
Purchase #2	$122.58	13.665%	$139.3306	$139.33	$139.35	$139.30
Purchase #3	$196.70	5.499%	$207.5165	$207.52	$207.50	$207.50
Purchase #4	$238.96	10.719%	$264.5741	$264.57	$264.55	$264.60
Purchase #5	$125.69	6.260%	$133.5582	$133.56	$133.55	$133.60
Purchase #6	$58.75	11.492%	$65.5016	$65.50	$65.50	$65.50
Purchase #7	$185.34	6.192%	$196.8163	$196.82	$196.80	$196.80
7 purchase totals =	$1,142.47		$1,248.0603	$1,248.06	$1,248.00	$1,248.10