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	$25.47	12.326%	$28.6094	$28.61	$28.60	$28.60
Purchase #2	$41.53	10.257%	$45.7897	$45.79	$45.80	$45.80
Purchase #3	$101.84	10.535%	$112.5688	$112.57	$112.55	$112.60
Purchase #4	$242.78	3.777%	$251.9498	$251.95	$251.95	$251.90
Purchase #5	$143.32	8.765%	$155.882	$155.88	$155.90	$155.90
Purchase #6	$187.95	4.464%	$196.3401	$196.34	$196.35	$196.30
Purchase #7	$180.95	4.746%	$189.5379	$189.54	$189.55	$189.50
7 purchase totals =	$923.84		$980.6777	$980.68	$980.70	$980.60