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	$35.76	12.808%	$40.3401	$40.34	$40.35	$40.30
Purchase #2	$244.67	4.537%	$255.7707	$255.77	$255.75	$255.80
Purchase #3	$45.27	13.364%	$51.3199	$51.32	$51.30	$51.30
Purchase #4	$196.42	5.545%	$207.3115	$207.31	$207.30	$207.30
Purchase #5	$232.35	13.864%	$264.563	$264.56	$264.55	$264.60
Purchase #6	$238.66	5.559%	$251.9271	$251.93	$251.95	$251.90
Purchase #7	$6.37	8.647%	$6.9208	$6.92	$6.90	$6.90
7 purchase totals =	$999.50		$1,078.1531	$1,078.15	$1,078.10	$1,078.10