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	$245.52	4.138%	$255.6796	$255.68	$255.70	$255.70
Purchase #2	$41.93	3.207%	$43.2747	$43.27	$43.25	$43.30
Purchase #3	$196.91	4.556%	$205.8812	$205.88	$205.90	$205.90
Purchase #4	$104.59	5.320%	$110.1542	$110.15	$110.15	$110.20
Purchase #5	$162.42	12.260%	$182.3327	$182.33	$182.35	$182.30
Purchase #6	$59.85	4.499%	$62.5427	$62.54	$62.55	$62.50
Purchase #7	$93.51	7.831%	$100.8328	$100.83	$100.85	$100.80
7 purchase totals =	$904.73		$960.6979	$960.68	$960.75	$960.70