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	$98.84	3.345%	$102.1462	$102.15	$102.15	$102.10
Purchase #2	$35.50	10.223%	$39.1292	$39.13	$39.15	$39.10
Purchase #3	$156.61	12.736%	$176.5558	$176.56	$176.55	$176.60
Purchase #4	$225.43	4.592%	$235.7817	$235.78	$235.80	$235.80
Purchase #5	$214.52	3.784%	$222.6374	$222.64	$222.65	$222.60
Purchase #6	$111.86	9.263%	$122.2216	$122.22	$122.20	$122.20
Purchase #7	$100.91	4.367%	$105.3167	$105.32	$105.30	$105.30
7 purchase totals =	$943.67		$1,003.7886	$1,003.80	$1,003.80	$1,003.70